secondary bilge pump
What you suggest doesn't make a lot of sense to me Carl. The usual purpose of a secondary pump if mounted higher, is to slow the rate of flooding in the event you get more water into the boat than the primary low pump can handle. The conventional wisdom is to mount the largest pump you can fit in a higher location.Also, the actual discharge rate of the pump is compromised by two things - the head the pump has to push against to raise the water out of the boat and the restriction of the hose size and type. Combining both pumps into one hose will decrease the capacity of both to pump the boat.For emergency purposes, mount the largest pump you can afford higher than the normally expected level water could reasonably be expected to reach and run that pump into a smooth hose (not the corrugated stuff) of equal or larger ID than the pump discharge fitting and don't use a check valve since it restricts flow and often gets stuck making the whole system inoperative.Also, keep in mind that the most frequently broken item in a boat is the float switch - you don't want to depend on one for two pumps.