Drilling a tank for overflows.

[fibinotchi]

When drilling a 55 gallon tank for an overflow, would it be better to have one big drain or two smaller drains, pump is rated at 800 gph and will only be about 4 feet from the top of the aquarium. Also would it be better to drain on one side and fill on the other side or drain in the middle.

 

[beaslbob]

I would make an overflow from pvc pipe instead of attampting to drill the 55g.
changes are the bottom glass is tempered ans will shatter when trying to drill.
my .pw

 

[fibinotchi]

I was thinking about drilling the back of it.

 

[saxman]

i'd run with two and use external Durso-style standpipes.

 

[fibinotchi]

So would I run two rated for at least 800 gph or what.

 

[saxman]

you'll need to figure out how much flow you're going to have returning to your tank, and match the outflows to that value. if in doubt, err on the side of the pump and bleed some flow back to the sump if necessary.
a single 1" O/F should give you about 300-400 gph. 1.25" will give you about 600 gph.

 

[number1gsxxr]

I would have two holes drilled even just to have one as an emergency backup. Less risk of flooding if one gets blocked. If it were me I'd probably go with (2) 1" drains. You can always slow one down a bit with a ball valve.
Online calculator for 800 gph says:
Recommended minimum drain pipe diameter = 1.17 inches
It doesn't really matter where you put the drains unless you are also using an internal overflow for surface skimming instead of using a simple strainer on the bulkhead. Most people choose the top center area of the back wall with the returns on either side. It really all depends on your preference and how you want to aquascape things.
If you're only going to go with one drain and one return I would put them on opposite sides so the return can help push water towards the drain for better skimming.

 

[wangotango]

Google glass-holes overflow boxes. They have kits that include the box, bulkhead, and a diamond-tipped hole cutter.
They've also got some nice videos about installation.