90 degree or T?

[nayrgaijin]

When you drill the back of a tank, what do you use to connect to the bulkhead? A T or 90 degree? Also why?

 

[Ian]

Use a T fitting, cap the top and drill a hole to allow easier flow...

 

[mfinn]

Where are you going to drill the hole?

On several tanks I've had ( 180g, 135g, 90g, 30g, and 20g) I drilled holes ( 2 on the bigger tanks) near the upper back corners.
On the inside of the tank I used a up turned pvc 90. On the outside I used a pvc T, with a piece of pvc that went up to about 2" above the top of the tank, with a pvc cap. Drilled a hole in the cap.
To keep fish and snails from going down the pvc 90, I used a small piece of gutter guard, rolled up and just pushed into the 90 opening. I've seen people make small overflows with pvc here also.
It's hard to gauge where exactly to drill the hole so the 90 works at the correct height for water level so I usually drilled the hole a inch or two low and used a short piece of pvc pipe in the 90 to get the perfect water height in the tank.
IMO go big on the bulkhead size. On my 180g and 135g tanks I used a pair of 2" bulkheads.
As long as you stay with a low flow through the sump ( 3x to 5x tank volume) these types of overflows are pretty quiet.
My 135g tank was 2' behind my couch in my living room where my family would sit every night.