Getting tank drilled for overflow.

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Ok I was planning on adding a ball valve. So I only need 1 hole drilled? What size is yours? Is 3/4" pvc enough?
I have a double overflow with one hole in each and they both enter in the refuge part of the sump. I did not build mine so I dont know what size but just looking at it it looks bigger than that.
Well it would look larger on the outside, its sized by the inside diameter.
Sorry I`m not good at DIY projects. I just have them built for me. Maybe someone who knows will tell us.
Np, thanks for all the help though. What type of media do you have in your overflow?
I assume your tank is acrylic and not glass if drilling. Most glass tanks use tempered glass on the bottom which can not be drilled.

The larger/smaller holes are so you can drain into one and return from the smaller hole not for draining from both holes. This is designed to be used with a completely closed canopy in which access from behind is limited.

You don’t have to have a return hole but if not then you have to have room behind the tank to run the return back into the tank.

Usually the standard sizes for the drain hole are either 1” which realistically gives you about 400 gph or 1 ½” which is closer to 800 gph. If getting it custom drilled I’d personally go for two 1.5” holes for draining and two ¾” to 1” for return to give you plenty of gph to play with.

Most sites say a 1” will give you 600 gph and a 1.5” gives you anywhere from 1200-1400 gph but I have never seen that much flow personally.

For return lines check out for great prices on Loc-Line.
Actually its glass and the bottom is tempered, but im going to be drilling the lower back just because of that.

Im going with 1" bulkhead because at 4' my return pump does around 400-500gph.
Since your drilling the side it should be ok but right away your dealing with 90 degree bends which will restrict your flow considerably. I’d keep that in mind since each bend will cut about 60-100 gph from your flow.

Are you going to use a Durso Standpipe?
Good point, I will take that into consideration when deciding the final size of the exit. I was also planning on using a standpipe. Im still waiting on my overflow to get here.
I have both tanks drilled in the upper corners and I get great flow to the sump. I have 1" bulk heads which need a 1 3/4" holes drilled in the tank. For the return to the tank I use a hang on back return elbow which is very easy to hook up to a pump and there is no extra drilling of the tank. Not sure why you would want to drill low in the back of the tank, do you plan on having a PVC pipe going up to the surface??
the way I have it set up I just use some PVC elbows and a plastic type screen on the elbows so no critters get into it. Very easy setup and easy to adjust for surface skimming and flow control. No big boxes or other plastic parts in the tank.
seaham, is that the setup in this photo?


I always wondered how the noise level was with that setup if it is.

Hmm....I really like that design....

Where did you get your bits? I have only really seen theglass hole bits online.
thats the 55, my 125 is the same. very little noise in both tanks, No gurgle at all just water noise. My return pump is what I hear more then the overflows.
You can adjust them so its easy to adjust to get rid of any gurgle. You need a good return pump to keep up with the flow also, if the water level drops this is when a gurgle can occur.
My 125 had some noise but it was a easy fix, I took a 12-15" piece of airline and stuffed it into the overflow through the screen and down the over flow so that only a 4" piece was sticking out. What this did was allow air to pass through the hole better and the gurgle was gone. This happened after i had to switch out my return pump and the new one had a lower flow rate.

I like the look of the tank with this set up.. No big items in the tank, no OF box to lose siphon.

Diamond bit hole saws can be bought on line in many places..
Before drilling check and make sure the tank is not tempered. I have a 55 that I got from walmart and myself and the LFS figured it was only tempered on the bottom... We'll we found out it was tempered glass on the whole tank... BOOM...
check with a Glass dealer in your area and see how much they will charge to drill a hole. Maybe worth it to have them do it with a drill press. Check around also, I had places tell me 50 a hole and I had others say 15.
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