[b_james]

The tank has a single corner overflow that both canister filters will draw from. Also the overflow will have an auto top off syetem installed to account for evaporation. If you plug the end of the suction line, the canister will go into negative pressure and will not have enough power to pump out water. Any water being pumped out will need either makeup water or air to account for displacement. Remember the canister is a sealed unit. The unit needs the help of syphoning to circulate. If you take the suction line out of the water, it will break the syphon and the pump will not have enough power to push the water up to the tank.. hence why we have to prime the canister if there is air in the line.