How to determine return pipe size

[scuglass]

ok im no expert but ive been reading alot lately for the overflow size if u want them quiet u should have them running at abou thalf capacity. sorry i forget the gph for teh different bulhead sizes. and for the return plumbing if u already have or know what pump u will be using id suggest going to rc and using ther calculators and fiddleing around with numbers and different options untill u get the most flow out of ur pump.

hpe this helps