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justDIY 06-02-2003 12:23 AM

reflections on diy overflow
I finally finished "fine" tuning my diy overflow project, which I had been working on for the past few weeks (a few hours here and there!)

I had set out to build a continuous siphon gravity overflow, rather then spend $50 - $70 for a pre-made injection molded model.

I built the skimmer and overflow tanks using food storage containers which are made from some sort of clear plastic. I picked them up at a local discount store (a 6 diff sizes pack for $8), and used a smaller and larger sized for the skimmer and overflow respectively.

I used a Plexiglas scrap bent into a U shape to bind the two containers together. At first I tried gluing the bracket onto the containers, but that proved to be impossible, as neither super glue nor two-part epoxy bonded strong enough for comfort. So I opted for tiny stainless steel nuts and bolts, and copious amounts of silicon caulk

The siphon tube (U-tube) is built from 3/4" sch 40 pvc pipe and elbows. I drilled top of the pipe and epoxied a check valve into the hole, to allow for starting the siphon.

Originally, I had designed the overflow to use 1/2" schedule 40 pipe for the stand tube, and 1/2" tubing to connect it with the sump, using mating 1/2" threaded plumbing parts and an o-ring to form a bulk-head in the overflow. The tubing ran into a 1/2" pvc ball valve, and then into the spray bar of my diy'd trickle filter (another post). In the bottom of the filter is a maxijet 1000 (~250 gph) pump, returning water to the tank via more 1/2" tubing.

This however, proved to be impossible to adjust. The pump was draining the filter faster than the overflow was filling it, and throttling the pump using valves resulted in a slow flood of the filter.

So, I took the overflow apart, and reamed the stand-pipe hole larger, to accommodate a ¾” bulk head, which consisted of a ¾” socket to ¾” MPT, an o-ring, and a ¾” FPT to ¾” socket. I then ran ¾” pipe through a few 45° elbows into a ¾” street to ½” fpt to connect with the valve on the filter. All this pipe is white schedule 40, although I may switch to gray schedule 40 (electrical conduit) for the pipe and fittings, since it’s less visible behind the tank, if/when I build another one of these.

After adjusting the height and design of the stand-pipe, I was able to operate the filter with the pump being supplied as fast as it drained (equilibrium).

The optimal design of the stand-pipe involved cutting it to be even with my ‘target’ water level for the tank, and then cutting four ¼” ‘teeth’ into it, which seem to avoid air-lock better than the smooth round surface of the pipe by itself.

I had originally intended to pre-filter in the overflow by using a sponge fitted over the stand-pipe. However, in a ‘power-failure’ simulation, I discovered the sponge was acting as a siphon, allowing the water level to be drained much lower than the stand-pipe’s opening. This is too bad, since the sponge was serving two purposes, first, it filtered large junk from the water, so trickle filter would seldom need maintenance on its bio-media, and secondly, it acted as a muffler to quiet the gurgling noise the stand-pipe makes. This aspect of the overflow will need more research; perhaps a coarser sponge would prevent siphoning but still make a decent pre-filter.

A second aspect that needs further refinement is the main siphon connecting the skimmer to the overflow. I had originally thought ¾” would be sufficient, since it can move a LOT of water under pressure. However, the main siphon is an equilibrium seeking siphon; hence it has very little pressure, so even the smallest obstruction causes noticeable reduction in volume. I think my next version will include 1” or 1½” main siphon (u-tube) and stand-pipe, to insure speedy delivery of water handle a more powerful pump.

Sorry for the long post … pictures may be coming soon, or I might just wait for version 2 of this project, since I don’t yet have digital.

Thoughts and comments would be appreciated. Questions are always welcome!


reefrunner69 06-02-2003 08:29 AM


So I opted for tiny stainless steel nuts and bolts, and copious amounts of silicon caulk
You should be able to find plastic screws and wingnuts at Home Depot, not sure how much they cost, but it would really save some stress if this is for a SW tank.

It sounds great!! I would definitely up the U tube and standpipe to 1" or 1.5", that way the limiting factor will be the pump rather than the overflow.

If possible rather than a standpipe to regulate the water level in the outside box of the overflow, you might consider a dam. Seperate the compartment to two halves, where the water flows into one half and then overflows the dam to go to the other half that contains the slotted stand pipe with the filter sponge. When power was lost, it would stop overflowing the **** and have a constant water level of that height.

Approximately how much did it ost to make this overflow?

justDIY 06-02-2003 11:39 AM

well, if I make another, here's the part list my current overflow uses

*skimmer and overflow parts
2x plastic food containers ........ $8 at discount store (you get enough to make two or three overflows)

1x 2 inch by 12 inch plexiglas strip ........ $free scrap from hardware store

8x 5mm stainless steel nut/bolt combos ......... $12 ouch! if they had anything cheaper, I deff would have bought them

*stand pipe parts
1x 3/4 inch socket to MPT coupler ......... $0.90

1x FPT to 3/4 inch socket coupler ......... $1.09

1x 3/4 inch rubber o-ring ........ $0.99

*siphon tube parts
2x 3/4 inch 90° elbows ....... $0.70

*general parts
10 ft 3/4 inch sch 40 pipe ........ $2.49 plenty for any small aquarium projects

All in all the project cost around $26 ... which is more than I thought I spent, I guess everything adds up quickly! ... Those bolts really hurt the budget ...

I would probably try using a glue again, since it's ideally leak-proof ... maybe I'll try using PVC pipe cement, since it actually _melts_ the plastic together, but it still relys on a very tight fit to begin with, I dunno

wingsfan 06-07-2003 12:13 AM

got any pictures of the overflow

justDIY 06-07-2003 01:54 AM

sorry, no ... besides, it's really ugly ;) ... nothing compared to what others have done with real plexiglas and a whole heap more skill then I got!

I might take some stills of it and scan them ... would be good to have a collection of pics of my various aquarium experiements, just for keepsakes in 20 years :)

I wish I had pics from my aquariums 20 years ago to compare with what I'm doing now

justDIY 07-24-2003 11:50 PM

I've got some pics of the overflow now....

inside skimmer box

outside drain box

Sorry! These aren't the best pics, the overflow is in use and working well at around 260 gph, and it's in a far back corner, hard to get to.

alrmc4 07-25-2003 08:10 AM

personally i am amazed at what you people can put together for your :thumb: selves wow

justDIY 07-25-2003 10:57 AM

thanks! :D

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