A long time ago, I saw a circuit using a silicon controlled rectifier
as a latching relay to control a bilge pump. It used two float switches
(one mounted higher than the other) and both had to be up to start the
bilge pump. The pump continued to run until the lower float switch
fell.

The advantages were that the back flow from the hoses did not cause the
pump to start again, and the low current demand allowed the switches to
last longer.

I cannot relocate the circuit,

Does this ring any bells? Anyone know where to find the diagram?

The only circuits I can come up with have the full pump current going
through the lower switch, unless I go to a mechanical relay.