Well, the input connections would presumably be:
So why not just put four hoses over the stern and cover it in a GRP moulding to hide them.
You then have the problem of what are you going to do with the output? Sink, watermaker
could be above the waterline but what about the heads?
You are also running long hoses around the boat, (up and down for a cat) so air locks etc. Failure on a long hose and you still sink.
If you goal is simplicity then half a dozen really good quality seacocks will outlast you, be simple to service
anywhere in the world, once a year. How often are you going to clean this space out to stop green things growing inside your tank.
Your "KISS" approach is likely to be far more complicated.