I would suggest that you not use the "normal" Auto-Off-Hold for Manual switch and use a On (Auto)-On (Manual) switch with no Off position instead. My reasoning is this: if your float switch fails and you do have unwanted water
in the bilge, you must stay by the normal, spring return, switch and hold it in the Manual position to pump the water
instead of looking for the source of water ingress. With the On-On switch, the operation of the pump is being controlled by one of two functions of the switch and can not be inadvertently turned off. Hence; the absence of the Off position in my scheme.
To secure power to the pump for service
, turn off its circuit breaker or remove the fuse. Speaking of fuses
and circuit breakers, ensure that you size these according to
the pump manufacturer's recommendations, and NOT in accordance with the ampacity rating table for the conductor.