yep! the over flow needs water to ... well, overflow into it, it can only drain to a certain point. The faster you pump water over that point, the faster it drains, back down to that point. I'd get a overflow with extra capacity, in case it get partially blocked it won't flood everything.
edit - just ordered some stuff from glass-holes.com and they rock! my bulkheads came with a tootsie roll!
edit - just ordered some stuff from glass-holes.com and they rock! my bulkheads came with a tootsie roll!
CRAP i wish i new that before >.<