Re: thru-hulls
There are two kinds of thru hulls; inexpensive plastic/nylon for use above the waterline (sink drains, gray water pump out, etc), and brass, bronze, or ss for use below the waterline (engine cooling, head flushing/pump out, live wells). Of course, the metal thru hulls can be used above the waterline, but never the plastic ones below the waterline
see CC Lancers comment above. If you use the plastic kind (above the waterline only!) you should paint it to protect it from uv. I dont like the plastic ones and prefer to use metal all around; ss above the waterline and bronze below.<br /><br />When using metal thru hulls below the waterline you need to be ever mindful of dissimilar metals and galvanic corrosion. The only thing that ever connects to a below-the-water-line thru hull inside the boat is a ball valve. Never connect plumbing or hose directly to a thru hull. All ball valves must be immediately accessible. Since bronze ball valves are commonly available, I use bronze thru hulls and avoid the whole issue with different metals. Also, all of my thru hulls have a nifty green AWG 10 wire connecting them to the boats bonding system.<br /><br />The ball valves need exercise and should be opened and closed several times a year so they dont get stuck in either orientation. Every couple years they need to be removed and inspected/rebuilt to replace the seal inside. So applying some non-conductive lubricant to the threads of the thru hull before fixing the ball valve to it is a good idea.