Notes:
Q1 = MPSA13 transistor
1K = brown black red gold
1M = brown black green gold

The water sensor is just a couple of small metal plates.

The relay needs to have a 6 volt coil and be able to handle the amperage of the pump.

The 6 volt circuit could be set up to run a different voltage circuit via the relay. We have been running everything on the ships at 6v to simplify the ships. There isn't anything in the rules that says you can't run the pumps on 120 volts AC. That doesn't mean that it makes sense......

Note: We have found that some of these circuits work perfectly, and some are very sensitive to being wet. Once there is water in the ship, the pump doesn't really want to shut off again. I believe that it makes a difference which of the sensors is in the bottom of the ship. I think the less than pure water in the ships is allowing current to flow from the battery directly to the pump sensor. Further testing is underway.

They also use a 12 volt circuit for 12 volt motors that does not need a relay.