I'm wondering if it's necessary to have flow across the bottom to blow the crap out from underneath the rocks or if it just needs to sit and wait to be siphoned? I know it should get overflowed is the best way but how do you guys (or girls) get the flow just right to move crap off the bottom to the overflows and not around the tank? My tank is a standard 180 72x24x24. Any insight is appreciated. Thanks, Sean.