Run a pressurized system, right?

How about a "bubbless" tank...or a Tetra tank? (bladder type? )
The pylon guys use them...you fill the tank with a big syringe, and I think there's only 1 line...somebody else who's into pylon might chime in here?

Edit: I edited out the V-30 pump/regulator part...thinking the vent would allow water to enter the system...but the snorkle sounds like an interesting idea...

There are a couple others here who also run boats...
Have you looked in the boats forum too? (probably a lot more "traffic" here though...)