I haven't seen where anyone mentioned the obvious - make sure your bilge
pumps and float switches (redundant) are in good working order. I keep my head valves (both) closed when the boat is sitting. I never close the raw water intake for fear of forgetting to open when I crank the engine
. I sail twice a week all year round.
If you are in a marina and have Wifi
, you can go to your nearest Lowes and purchase
a $179 IRIS system that will text and call you if it senses water. You can add a camera
to the system for another $100 and take a peek whenever you want from your Iphone
There is a wealth of information on the internet
on how to plumb a a toilet with an anti-siphon loop.