Open and close often
We have the following on our 40.5, not including transducers, vents, and bilge pumps:Forward head intakeForward sink drainGalley sink drainAft head intakeAft sink drainMaceratorRaw water intakeWe always close all of the seacocks when we are not on the boat. This does add about 3 minutes to the "leaving the boat" process, but it allows me to sleep better. To keep from accidently starting the engine with a closed seacock, I tie the igition key to the closed seacock. We have a friend at our yacht club that left his boat for less than 30 minutes (without closing his engine seacock). One of his fairly new hoses in the engine decided to leak and siphoned in enough water to sink the boat in the slip.