Size of sump for 90 G ?

[Chin_Lee]

Regal
consider adding overflows to your tank by having some pieces of glass cut at a local glass store. Then just silicone them into place after you've got the holes drilled. Cheap and probably won't cost you more than $40 in glass and labour.
Is your glass tempered at the bottom? Are you planning to drill the side or bottom (if its not tempered)? the rate your bulkheads will drain the water will depend where its located on the tank. This is because if you have it lower in the overflow, it will have higher water head pressure causing it to drain faster. If its higher in the overflow, it will drain slower due to lack of head water pressure.

[Regal]

The bottom of the tank is tempered so the bulkheads will be going on the back glass of the tank around mid-section, the water will come back out from piping above the tank.

[Regal]

I am getting the glass cut this weekend, would a single 2 " bulkhead be enough for drainage if the bulkhead is one the side of the glass, not from the bottom?

[untamed]

It is fine to have the holes in the backwall of the tank. You haven't mentioned it, but you need to build an overflow box inside the tank. I think you'll need an overflow box that has top edges that total nearly 2 feet for that kind of flow rate.

As for hole size bigger is better. 1.5" might work, but 2" is better. If you make the first hole 2", you could make the 2nd hole 1.5".

Make two holes. Make 2 holes. You have only this chance to do this right and the best advice we can provide is to make two holes while you have the chance. That or live with the noise and don't come back asking how you can make it quieter....because then we will say...you should have made two holes!!!

Both holes have to be in the same overflow box.

Finally...I should mention that you should drill 2 holes....