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Overflow Boxes


Dec 30, 2005
I have a couple questions conscerning an overflow box since i am about to construct a wet-dry filter out of a 20 gallon and wanted to avoid any drilling on the tank that i can.

First off, is it possible to construct your own overflow box or do you need to buy them? If it is possible, how hard is it and what materials are we looking at? Cost of materials?

Second, if you can not make your own and you have to buy, what is the cheapest choice? so far all of the ones i have come accross are at least 75$ which is a little bit to pricey in my view. Links and such would be appreciated here.
Its possible to build your own hang-on-back overflow, but only if you feel comfortable cutting acrylic with a router, bending it with a torch, and welding it with a solvent. Drilling a tank is a much simpler do-it-yourself project.

There's a lot of different overflows commercially available, and they run from being pretty reliable to absolutely worthless.

Here's a couple examples of bad overflow design:

Silent Overflow Skimmer

Continuous Siphon Overflow

Overflows typically always have an internal and an external box, connected by a siphon tube. Both of these examples have one thing in common: the siphon tube is wide, flat and skinny. This allows bubbles to get captured inside easily and considerably increases the chances of an overflow failure (something you do NOT want to happen). I owned the first overflow shown and there was pretty much always a bubble inside.

Here's a couple examples of good overflow design:

Lifereef overflows


The siphon tubes in both these overflows are cylindrical and less likely to collect bubbles. People have had good luck with the Lifereef overflow particularly. No hang-on-back unit (or really any overflow at all) is foolproof, so I would get in the habit of taking a quick look at it every day just to make sure its running OK.

Good luck,

Thanks Dan, but now that you have mentioned drilling in a new light, could you explain a little more on how or what you would do for a project like that. I am now a little undecisive if i want to go for a hole or a box so if you had a personal reccomendation i would be interested.

thanks again,
I to would recommend drilling the tank. Its much easier then most people think. I just drilled my 150 which is 1/2 inch thick glass. Took me about 25 minutes to do 2 holes with a coordless drill.

You can buy the drill hole saw from ebay for about 15-20 dollars shipped. Be sure its the size that will fit the bulkhead you need. Determine if you are dealing with a tempered glass bottom by checking the manufacturers web site. I had to drill the back of the tank because of this. When ready to drill, If you do not have a drill guide, it is a good idea to drill a thin piece of wood, to use as a guide to start the hole or the bit will skip and possibly scratch the glass. Also, to reduce heat, you can make a small damn around the area to be drilled with a putty and fill it with water. Place tape or even a piece a wood on the other side of the glass for when the drill is almsot through, the weight of piece of glass your drilling out will break before the drill is all the way through which can cause a chip. Once all prepared, just drill through. Dont use too much pressure and your good to go. For the overflow, you can just get some pieces of acrylic cut and then silicone to the tank and your done.

This is a much better option then a hang on the back overflow...
hmm ok. It's just that the tank currently has water in it and I was just planning on throwing on the overflow box so I wouldn't have to drain the tank out (which has been cycling for quite a long time now) and take out all of the fish inside.

However, if both of you reccomend drilling I guess it wouldn't be that hard to do I just dont know what kind of drill bit I would use to drill glass.
Drilling isn't that tough of a project--but with any DIY project you do want to make sure you're up to it before you risk your aquarium. Don't let us pressure you into it if you're not comfortable with it. The bit you need is a diamond-coated hole saw. They're available on eBay.

The trick is to keep the diamond bit wet. If you do it outside you can just tape the end of a garden hose to the glass near where the hole will be and set it to trickle. Paradox's dam method (that damn method!) works fine indoors. Remember that the size of the hole is going to be larger than the pipe size of the bulkhead: a bulkhead for a 1" PVC pipe is going to require a hole that's about 1-3/4" or ~45mm.

The most important thing to do is to plan ahead. Know what your overflow is going to look like. If you want to make a "megaflow" style overflow like most factory aquariums have, you can order just the black acrylic piece, drill a couple holes and silicone it in place. Or you can plan the box yourself and get a few pieces of 1/4" glass cut locally, then silicone them together to make your own box. Just this week there's a thread on Reef Central's DIY forum about internal boxes.
Make your own!

I made my own overflow, and it worked great, here is a picture.. it want lose its siphone if the power goes out.. it is currently not being used since i dont have a large tank anymore... but it will be back in one VERY shortly,. anyways there is directions on building this thing all over the internet, just google DIY overflow, and you will find it..


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I'd say you're flirting with disaster there. We can say as a matter of scientific fact that there are bubbles inside the siphon part, but more importantly there's no way for you to know how big they are or how close you may be to a failure. The round-section u-tube in a commercial overflow has smooth sides, but the problem with using PVC is the width of the tube changes: its narrow in the middle, and wider at each elbow fitting. When the water is traveling through the pipe and then enters a wider area the velocity slows down and an air bubble forms. In this overflow, there are five places where that's happening. In four of those places, the natural flow of water will tend to push the bubble towards the top of the siphon: the absolute last place you want it. What makes this so dangerous is that the entire apparatus is opaque so you have no clue how close it is to disaster at any given time. I wouldn't recommend Marineboy do anything so reckless.

I never had any trouble with it, even after power outages, when the sump pump turned back on it would start right back up with it, a lot of people put a one way air valve in the top of the overflow so they can suck any air that accumilates in there out, but like i said i never had any trouble, it ran for something like two years and i only restarted it maybe 3 times, not to any error on its part but to me removing for whatever reasons, anyways, i have plenty of faith in them, more then i do in a drill bit, when i get my new tank i plan on having it pre drilled, but i just couldnt risk drilling my own. i agree a drilled tank is better, but its to much risk for me.
Putting an air valve just adds complexity IMO: just one more place for a leak to form. Like the CSS skimmers that require an Aqualifter pump to operate: they make it sound like they're adding a level of redundancy, but when you look at it from an engineering perspective, they're actually removing fault tolerance.

Drilling really isn't tough. I've done about seven holes now. The technique that hobbyists use is exactly the same as the manufacturers do. I've been drilling just about everything in my house besides the aquarium--I put my dryer vent through a basement window rather than poking holes and chiseling out foundation!

It never would have even occurred to me to drill a hole in a window for a dryer vent! Replacing the glass for an AC unit, yes, but drilling a window is definitely original.
As a tool using species, we can use tools to extend our ability to assert our wills upon the world. Frequently, this involves making holes in the world. :biggrin2:

(personally, I just found out that DeWalt has a good chop saw for only $200, so I can now assert my will to make cross-cuts on 2x4s rather than making holes. It doesn't have the radial arm slider, or the laser targeting system, but those probably would have pushed it out of my price range.)

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