The key is to rotate the pump so the cord is nearest the cord slot, this way it has a lower profile and less touches the bottom housing, you have to make sure the output is fully inserted in the clear jet pipe. If the pump is in properly, only a small portion of the impeller housing will touch the bottom plate. It can be helpful to have the front output grate removed as you can then see that the pump is fully inserted, the intake should almost be to the top of the D shaped cut out for it.