Broken Pump and replumbing Sump

[Cal_stir]

I use a combination of pvc and hose, my drains are 1 1\2" tigerflex(it can be glued to PVC fittings), my pump in is PVC with a rubber coupling for vibration, my pump out is a PVC ball valve with tigerflex from the ball valve to a PVC header, there I branch off with hose to my returns in the tank.
A 20 gallon sump can't afford you much flow, about 400 to 500 GPH(IMO), the rest of the flow would have to be accomplished with powerheads or a closedloop circuit.
Plumb your pump in with a valve that allows you to bypass the returns and go back to the sump, that way if your pump is to big you can control the flow with the bypass, I prefer to run my pumps full open, and if you do cut it back always cut back the outlet never restrict the inlet.
I never shut my pumps off, I put them in bypass.