Thru hulls?

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Do you guys put seacocks on all your thru hulls that are below the waterline?
My 18 has the livewell overflow and drain going straight out the transom without valves.
I'm thinking of replacing the plastic factory ones with some stainless ones from Gem and want to get the right ones (threaded for valves or just barbed).
Because the overflow always allows water in, a valve to shut it off completely will solve that problem.
I know there's a huge safety factor in having them but the darn valves are an arm & leg!