The Quick and Easy Aquarium Overflow

At some point in the fish aquarium hobby you may realize that you can build a better aquarium filter for less money than it would cost you to buy one from your local fish store. While some of us will succeed, some of us will fail miserably and will instead spend a fortune on what becomes the newest curbside addition on garbage day.You may decide to run a water line from your aquarium to an external filter such as a sump pump or a wet/dry filter system. There are basically two methods on how to run a water line to your aquarium:

  1. Drill holes in the aquarium and install bulkheads
  2. Buy an expensive overflow box

In the first method, water flows out of the aquarium through the bulkheads. The major problem with this method is if you ever plan on selling the aquarium, unsightly holes can possibly limit the sale. Since most store bought aquariums are sold without any holes to run plumbing, have the aquarium pre-drilled with holes before buying it to save you the hassle later.

In the second method, the overflow box brings water over the edge of the aquarium and into a sump or wet/dry filter system using a siphon. Although this is a good system, it can be very expensive, especially for people who own several aquariums. The cost for an overflow box starts at around $60. This leaves us with the mysterious “overflow”.

So what are my options?

With what seems like magic, a siphon overflow can move hundreds of gallons of water out of your aquarium using nothing but the power of gravity. No pumps. “Well, anybody can siphon water out of aquarium” you say. “Just suck on the hose!” Yes this is true, but you need a controlled siphon to set the water level of the aquarium.

Your aquarium must also be able to handle an increased flow from your sump pump return line and whenever you add water to the aquarium. It’s also important to make sure that the siphon is not broken in the event of a power failure. Should your return pump turn on once power is restored, the siphon must be able to stay primed so that the aquarium doesn’t fill up and pour water all over your floor instead of down into your sump.

There are many ways to build an aquarium overflow. More wrong than there are right I reckon. While this may not be the final version of this particular overflow system, I’m sure it’s far from perfect, but one thing it is, is cheap! I would encourage you the reader to improve on its design and post your trials on our forums.

Materials required:

  • PVC tube (at least the height of your aquarium)
  • 1″ clear vinyl tubing, or comparable flexible food safe tubing
  • handful of 1″ drain or bulkhead fittings
  • 2-liter plastic juice jug with an open handle
  • 1/8″ hose from an air pump
  • water proof silicone (depending on the quality of your drain fittings)
  • one or two empty plastic aquarium plant baskets
  • one black zip tie

Tools required:

  • drill with a 1″ wide bit, or hole saw
  • sharp knife or garden shears
  • saw for cutting PVC
  • tape measure

Part One: Measuring the desired water height

  1. Using a tape measure, record the maximum height that you would like to fill your aquarium before the water exits the aquarium. I like to have my aquarium’s water level about an inch and a half from the brim.
  2. Put the plastic or PVC end cap on the end of your PVC tube. This end will sit on the bare aquarium bottom.
  3. Mark the water height on your PVC tube and make a straight cut through the tube.

Part Two: Creating a water diffuser and fish catcher

  1. Take your plastic aquarium plant basket and cut a hole in the bottom (about the size your vinyl tubing).
  2. Zip tie the basket to the uncapped end of the PVC tube. You should be able to snip some of the links and “undo” the basket. Add a second plant basket to complete the circumference of the tube. This should keep any fishes out of your filter, so make sure you can improvise a grill capable of keeping your small fish and fry out.

You can also use some needle point grid to make a diffuser. Simply wrap it around the PVC tube and secure it with a couple of zip ties.

This water diffuser works by drawing surface water into the upright tube as it is drained out by the vinyl tube, effectively “skimming” the surface. This is the best way to keep protein buildup or oily patches from blocking the oxygen exchange along the water’s surface. After your set up, you can observe the surface particles being pulled from across the aquarium and disappear into the upright tube.

Part Three: Building a juice bucket drain

It took me some time to think of the right materials to build this. I have seen these made from acrylic, and thought, “there has to be an easier way” and by easier I meant cheaper. Here it is.

  1. Find a juice jug with an open handle that can hang on the edge of your aquarium.
  2. Drill a hole in the bottom of your juice jug. You will want to do this from the outside bottom very carefully. If you place too much pressure, you will crack the plastic.
  3. Install your drain fitting so that the water level in the bucket will always be at least one inch. This will maintain your siphon if the power goes out and will allow the water to drain once the water starts pumping into the aquarium again.

Note: I used a rubber washer on the inside of the bucket to make sure there was a water tight seal. You may need to use some silicone, let the silicone dry before proceeding to the next part.

Depending on the direction of your sump, install the appropriate bulkhead fitting to the outside of the jug.

Part Four: Putting it all together

  1. Submerse your upright PVC tube in the corner or center, along the back wall of the aquarium.
  2. Hook the handle of the juice jug over the edge of the aquarium and into the mouth of the upright tube to secure it all in place.
  3. Take a length of vinyl hose comparable to the distance needed to join the two pieces you’ve just made.
  4. Insert one end of the vinyl hose at least half way into the PVC upright tube and bend the other down into your juice jug/drain.
  5. Insert a length of air pump hose halfway into the vinyl hose on the “jug” side.
  6. Once your drain is connected to your sump, pour a cup of water into the juice jug to prime it.

Note: The vinyl hose should be loose and submersed in bottom of the jug.

You are now ready to start your creation. Apply a little suction to the other end of the air pump hose to draw the water out of the aquarium initially. If you’re too afraid of using lung power for fear of catching some jungle parasite, you can always attach it to a venturi hose on an extra power head to start the siphon.


40 Responses to “The Quick and Easy Aquarium Overflow”

  1. The Professor on 11 Oct 2007 at 9:55 pm #That looks pretty cool.
  2. W on 01 Dec 2007 at 4:08 am #A simple modification is to drill a tiny hole in the top of the flexible tubing. Then attach a air hose check valve so the air can only go out the top of the curved tube. Then you attach your air hose from their to the venturi input on your powerhead.Then if you have a power outage and loose the siphon, when the power kicks back on, the powerhead will restart the siphon automatically– guarding you against the mess of an overflow.
  3. Marcel on 03 Dec 2007 at 5:44 pm #I have seen the modification you speak of, but i assure you, this system will not lose siphon in the event of a power failure. I do how ever feel that attaching the power head is far better than accidentally getting a mouth full of tank water when starting the siphon! LOL Thanks!
  4. mark godfrey on 05 Jan 2008 at 9:39 pm #I am still confused on how the siphon would restart. When you lose power, the tank will drain down to below the intake of the flex tubing, and you’ll get air in it. Even with a purchased overflow box then the box will just drain down and the same thing will happen.I just took back my overflow and installed a new tank with an internal box, that is the only way I could be sure. Lots of work.
  5. Marcel on 06 Jan 2008 at 7:47 pm #The siphon never breaks because of the equalized water pressure between the pvc tube and the 1 1/2 inches water that is always in the drain bucket. Every time I do a water change the tank level drops well below the PVC intake and the siphon stops, not breaks. The water is still in vacuum in the clear tube. When i add water to the tank it “overflows” into the PVC tube, and restarts the siphon. This is very much like having an internal box, the principals are all the same.
  6. mark godfrey on 09 Feb 2008 at 6:07 pm #Thanks for the reply Marcel, I’ll look into that. I have a basement sump that I want to overflow into a container to put a set-in protein skimmer in, I don’t want to take up a bunch of space in my refugium.Thanks again!
  7. Marcel on 23 Feb 2008 at 4:04 am #No problem Mark! I’d love to share some ideas. Part of the thing i like about this setup is there is minimal equipment showing inside the tank. The PVC tube is so easy to disguise as well. You can cover it in silicone, then roll it in sand or just let the algae grow in. There is a thread in the forum on modifications. Let me know if you have anymore questions.
  8. Kyle on 23 Feb 2008 at 7:15 pm #Have you figured out what kind of flow rate you can get with this setup? I love the simplicity and cost savings of
    your design.
  9. Marcel on 28 Feb 2008 at 10:30 pm #Thanks Kyle!
    I’m not sure how many GPH this setup is capable of, with the listed pipe an hose sizes. But for reference in my sump I have a larger return pump, a powerhead actually rated for a 100 gallon tank at ~ 4-5 foot head, the water is coming out like a garden hose. When i add a 5 gal bucket during water changes it’s possible to “max out” the draining capabilities, but it soon catches up.
    In other words the limiting factor is how much water you can return to the tank via the sump pump. I may try adding a second pump to see if it can handle it the flow. Of course this project is entirely scalable, if I had a bigger setup I would build a bigger model!
  10. Kyle on 01 Mar 2008 at 7:01 pm #Thanks for the reply. Im trying to decide if I want to go with a sump or build an overtank dump filter. The possible disasters of the sump kind of scare me.
  11. Kyle on 23 Mar 2008 at 9:43 pm #Well I went with the design. The only thing I changed was I made the U tube out of PVC. The hose I had would not bend without kinking. I have had it running for almost 2 weeks and all is well. Thanks for a great idea.
  12. Marcel on 01 Apr 2008 at 1:37 am #Great Kyle! Yeah a PVC U would probably work great. Definitely would last longer. What size of pipe did you use? Any chance you could post a pic?
  13. Kyle on 02 Apr 2008 at 11:13 pm #I used 1 inch PVC to make my tube. I have a pump that does about 400 gph and it matches up really well. Here are a couple pictures.

  14. Kyle on 02 Apr 2008 at 11:27 pm #Here are 2 pix of the 3 inch tube inside the tank.
  15. dave on 06 Apr 2008 at 5:36 am #hi. neat design. i’m new to this and i was wonder what is the 1/8th inch vinyl tubing is used for. thanks.
  16. Marcel on 06 Apr 2008 at 5:40 pm #Very nice Kyle! Thanks for posting the pics, the 3 inch PVC tube looks very inconspicuous in your tank. Good show!Dave: the 1/8″ tubing is for starting the siphon, you can see it inside the 1″ “U” tube.
  17. Kyle on 06 Apr 2008 at 9:25 pm #I thank you for the design. I have four tanks set up. I have always wanted a wet dry setup but didn’t want to upset my very understanding wife. She has been very patient with me in this hoby. I didn’t want to spend $200 or more on a wet dry setup. I have about $80 dollars into my setup and it works very well. So once again thanks for your design Marcel.
  18. Marcel on 09 Apr 2008 at 9:32 pm #I can relate Kyle! People sometimes fall into the marketing traps out there. There is a commercial solution to everything fish related now days and often the costs are steep. I really enjoy fabricating projects, most of the time you save money, and the other times, well… you know…. it’s a learning experience :) I’d much rather spend the money on fish than on fancy equipment! Thanks for all your comments!
  19. dave on 10 Apr 2008 at 7:21 am #thanks marcel!do you know where i can get some info on sump tanks/ setups? i have been researching but i haven’t found any good stuff. thanks in advance.
  20. Marcel on 10 Apr 2008 at 3:48 pm #Dave are you looking for a DIY sump? I’ve built a few in my day. I’ll see if i can dig up some pics or ideas.
  21. Maureen on 04 May 2008 at 6:14 pm #Hi I am totally new to this and want to build an EASY sump. I get the overflow basics, and maybe I’m an idiot…but what is the air tube for??? Also do you have a really simple plan for a 10 gallon sump for 55 gal tank? thanks
  22. Marcel on 05 May 2008 at 3:53 pm #Hi Maureen,
    The air tube is for starting the siphon. You can suck the air out with your mouth, or alternatively you can attached the air hose to the Venturi on a power head.
    I do have a simple design for 55gal. tank with 10gal. sump, that will be posted in the near future so stay tuned! Thanks for taking the time to post!
  23. John on 13 May 2008 at 9:33 pm #Hallo , i have only one question about the over-flow!By the way is pretty cool!I can’t understand how far inside the PVC tube goes the clear vinyl tubing!Thx for your time and looking forward to hear so i can start one too!
  24. Marcel on 14 May 2008 at 5:03 pm #Hi John,
    The clear vinyl tube goes about half way to 3/4 of the way down the PVC tube. Good luck!
  25. Ray on 19 Jun 2008 at 5:35 am #A nce device for cheap! (It would be a nice device for not cheap with trick parts…)A nice article too. It is a good demonstration of the applied mechanics of a siphon overflow. You have good ’street smarts’ for the mechanics, that sadly some of the rest of us lack. What would make this article complete would be a schematic (with measurements) to get a clear picture of exactly how the parts fit together.

    Also, you mention that the design would effectivly scale, and I believe that is so. It would be great to hear your thinking on scaling it to multi-overflow, multi drain confiurations for the big rigs out there. …and one to fit us nano-dwellers. Do you have a design that would work with a tea mug instead of a juice jug?

    This page is in my favorites.


  26. Marcel on 19 Jun 2008 at 7:41 pm #Thanks ray!
    I appreciate the comments! I have a “part 2″ article in the works that should address some of your concerns about larger and smaller setups and how to connect it all to a sump or wet/dry. Stay tunned!-=Marcel=-
  27. Maureen on 05 Jul 2008 at 3:25 pm #ok I finally got my overflow set up and it works great. However, now I have all this annoying gurgling sound. Is there any way to reduce this? thanks
  28. Marcel on 07 Jul 2008 at 4:17 pm #Hi Maureen,There are at least two ways to quiet the overflow. One is to cover the drain pipe with a foam block this will stop the “whirlpool gurgle, you may have to rinse this out periodically. Alternatively you can attach another bit of pipe to the drain inside the juice bucket in the shape of an inverted “U”. This way the water is “pulled” up into the elbow before it can start gurgling. I’ll try and get some pictures to accompany all these mods :)
  29. dave on 10 Aug 2008 at 10:09 am #thanks marcel!Yes. I am trying to build an DIY sump.

    it would be nice of you if you can help me find some pictures or ideas.

    I tried to design a sump that will use gravity to pull the water through a series of filters, carbon, and bio media. i haven’t build one yet. but i would be glad to hear your comment. thanks.

  30. Clay on 11 Aug 2008 at 3:42 pm #great article, simple design! there are 2 keys to your overflow not breaking a siphon during a power off or otherwise: you said to place the hose at least half way down the pvc tube AND place the other end in the jug. by placing one end of the hose half way down the pvc, it places it BELOW the bottom of the external jug (key #1). if placed too high, the siphon will pull too much water out of the pvc overflow and air will enter a break the siphon. the other important direction that was only implied, is that the other end of the hose (in the jug) must be BELOW the top of the drain fitting so that it is always immersed in water. (thus when you prime the system with your cup of water, this water needs to cover the bottom of the hose, otherwise it won’t work.) If the hose slips and ever moves above the top of the drain fitting, air will enter the system when the water subsides during a power off of the return pumps and it won’t restart. the rest is all physics – turn off the return pump and water will siphon and drain into your sump until the water inside of the pvc and the external jug hit the same equilibrium level equal to the top of the drain fitting. when it hits this point, water will no longer drain into the jug and it will also not drain backwards from the jug into the pvc.the only danger is if the power is off long enough that water in the jug evaporates below the hose end – but I would think your siphon is the last thing you’ll be worried about if you have a power off that long!

    also, don’t forget to keep the free end of your air line above the end inside the vinyl hose, or you’ll get a second siphon going that could get messy!

  31. Bigworm175 on 21 Sep 2008 at 9:56 pm #I just finished making this overflow that feeds a 10 gallon sump/fuge/place for my equipment. This was not very hard and MUCH cheaper than a commercial product that does the same thing. My reef is now much less cluttered with equipment, I have a place for water changes, and it added about 8 gallons to my total water volume. I also love the surface skimming that skimms the scum form the surface and allows more light to reach my corals. Great design! Thanks!
  32. daminh on 24 Sep 2008 at 1:04 am #I have a 29 gallon tank with a HOB filter made by CPR. Any ideas on how I can make an overflow system for this?
  33. Marcel on 26 Sep 2008 at 3:36 pm #Thanks Bigworm175! Glad you like it! Did you get any pictures? I’d like to start a gallery of other people’s versions.Daminh, I would not try any modify the the HOB, the plastic is too brittle to cut or drill, and glue never sticks either. This system will work fine on a 29 Gal. I’d say use a 10 gal. glass tank or decent sized Plastic Bin as your sump while you experiment. Good luck!
  34. Paul on 05 Oct 2008 at 3:39 pm #Can you please explain how the siphon will not break? Sorry if I sound stupid but i’m a little confused ;) Diagrams would help. thanks!
  35. Marcel on 06 Oct 2008 at 5:35 pm #Thanks for reading Paul,
    there is a good diagram made by Rob_Bozuk in the canada fish tank forums here,,9.0.html.The siphon will not break because once the water pressure has reached equilibrium in the jug vs the pvc tube, no water will flow out of the tank until more has been pumped into the aquarium.
  36. TOD on 22 Nov 2008 at 4:51 am #I am new to the diy overflow, but i made one of these designs the other day and it works but i need to use bigger pipe to get enough flow to match my pump. anyway i was thinking that it would be easier to just put a bucket under the tank on top of sump/ refugium and have drain hole in bucket same as pichter and drain right into sump/refugium. wouldnt that work and create a stronger syphon with the tank drain well below the tank? or am i not seeing the big picture. it cant overflow your bucket since water will stop draining at desired water level. seems to me this would work and give more options instead of trying to find something that fits behing your tank. PLEASE let me know if there is something i am not seeing so i dont flood my home. 8-) TKS
  37. Marcel on 24 Nov 2008 at 5:27 pm #Hi tod, I think your system would work. I would pay close attention to the water levels when you pull the power plug. Starting the siphon initially may be more difficult since there is so much more vacuum needed to start the flow. Make sure you have a bulkhead in the bucket as well to keep the water level in the bucket at around 1 inch deep, this should maintain your siphon.I’m really interested to see how it works, please post your results! The biggest complaint so far has been that the over flow takes up too much room, so if this works people may have another option.

    Thanks again Tod! Lets see the pics!

  38. ha hahhhhahaha on 10 Dec 2008 at 1:54 am #i am from New Jersey but wow. that is ghetto. i have one pretty ghetto but you beat me hands down. i am sure it functions very well and a good thing it hangs on the back so it’s not in your face…. lol happy fish keeping
  39. Christobal on 21 Dec 2008 at 12:52 am #Instead of using the water diffuser I drilled 1/4” holes around the PVC at the level I wanted. I don’t know if this limits the flow though…
  40. Marcel on 08 Jan 2009 at 8:55 pm #Christobal, that is the best idea yet for the diffuser! Kudo’s and thanks for posting!

1 comment

  1. Lars-olof July 31, 2012 10:37 am  Reply

    I want a Blood Parrot Cichlid fish sooo bad! They smile! Who doesn’t want a smiling fish?!

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