Size of sump for 90 G ?

[Chin_Lee]

at 2600 gph, i would be most concern about water noise from the overflow and drains.
I would consider 1.5" min and possibly 2".
If I were in your shoes, I would have 2 x 1.5" holes using the herbie method for dead quiet drainage.
The good thing with the dart pump is you can restrict the output without any damage to the pump. So if the 1.5" drain cannot handle the flow (which I doubt) you can tone down the output further until it can handle it. 2600 gph is a little high for a return through the sump unless you are planning to use the flow from the return as your primary source of circulation.