i've been reading post about diy wet/dry filters and im wondering if you need a pump to send the water from the sump(?).back to the tank??i was picturing it as like a canister filter..where its all sealed up but the in coming and outgoing holes..so when the water comes down from the tank and fills up the [canister,sump], the waters coming too strong that it'll send the water back up to the tank..is this what happens??or do you need an electrical pump to make it work??