Bulkhead sizes & flowrates

[TheReefGeek]

A 2.5" hole will fit a 1.5" bulkhead, this is what I use.

What flow rate info are you looking for? Draining capability? Or pumping capability, because these two figures vary greatly.

For drain lines I would double up on the drain lines, but only pump what 1 can handle, so you have built in fail-safe.

I wouldn't push more than 800gph through a 2x 1.5" bulkhead, assuming you are using a durson standpipe or similar. Yes it is possible to do more, but why push it? Get most of your flow from a closed loop, and just flow enough water for 10x - 15x turnover in your sump, otherwise you might run into microbubble trouble.

On the pumping side, 1.5" can handle a lot of flow, I know my barracuda with a 1.5" outlet is 4500gph with no head pressure.