Teflon is also acceptable. Make sure two stainless steel hose clamps are used to secure on the hose. Finally, a soft wood plug tied next to the seacock is excellent insurance against an unexpected catastrophe. This should be done with the seacock open, or the grease will just empty into the hole. Defining a Proper Seacock All thru-hulls below or near the waterline must have a valve that can be closed in an emergency or when the boat will be left unattended for more than a few days.
Gate valves have internal parts that deteriorate and snap off.
Even turning the wheel will not confirm that the valve is closed. The internal mechanism could have become jammed open by debris, for example, but feel as though it had been closed. Plastic seacocks are brittle and can be easily broken by an errant foot or a stowed anchor. While probably not as prone to mechanical freezing as their bronze counterparts, Marelon seacocks must also be taken apart, inspected, and lubricated periodically. These newer valves are acceptable, especially if they have a flanged base and are mounted on a backing block.