Hot Water Source for Shower in Closed Cooling

Well, I didn't get a super close-up, but some years ago a fella had set up a hot-tub. Tub filled w/ Delta water, then heated with a coil of copper tubing carrying hot engine water. Genius.

I may have come up with a potential source for hot water and a shower upgrade.  As stated above, my 206 Ski Nautique has the closed cooling (aka freshwater cooling) and no obvious hot water source for a shower.  So, after poking around a bit, this is what I came up with.  There are 2 vertical brass drain plugs in each exhaust manifold -- used for winterization.  After pulling the boat off the lake, I removed one of these brass plugs.  HOT water came pouring out.  So...here is my idea -- replace one of the drain plugs on each manifold with a brass NPT fitting with a hose barb.  Run these hoses into a Tee and then to the shower valve.  I would have to put a strainer assembly prior to the shower valve as the water from the manifolds can have some metal flakes, rust and other gunk.  I can tap into the pressurized side of the raw water feed before it makes its way into the heat exchanger.  This could be the cold water source.