Depends on what you are trying to attach to your manifold. You will need to figure out the GPH of everything that will be attached to the manifold. If you don't have it you will need to find it. Then that plus the amount of water needed for your return pump to keep water moving between the tank and the sump will give you your total GPH needed. With that number in hand, you will be able to look at prospective pumps objectively and see if the pumps satisfy your expected GPH need.