[Chris Burkard]

That black cylinder is likely a pressure tank (pulse regulator). The filter is usually located on the suction side of the pump and is small with a clear spin off cover and stainless screen inside. I believe it is designed to reduce the pulsing sensation created by these smaller pulse style water pumps. I'm not sure which pump would be an easy replacement and give you better flow and pressure. I would look up Shurflow pumps and see what they offer that is of similar size and inlet and outlet diameters that gives you more flow and pressure.