I know this has been asked here before, even by me...
but it's back on the To-Do list so I want to get information
and opinions again:

I'd like to install some kind of valve setup so that my raw-water
intake for my engine cooling can come from the sea-water
scoop or from a garden hose.

Our situation is that we have a gas powered 6-cylinder engine
that is direct raw water cooled. (No heat exchanger...the water
just runs through the engine and out the exhause.) It's simple,
the water pump just pulls water from the ocean and pumps it
into the engine. There is a hose from the pump down to the
through hull.

What I'm thinking is I'd like a "Y" or "T" type valve such that:
Port A - the one to the water pump - is always open
Port B - Goes to the lake / ocean - Is open when C is closed.
Port C - Goes to a fitting for a garden hose - Is open when B is closed

What is the best valve / sources for valves for this?
It's probably going to be below water-line, so needs to be very secure?
I think when I saw them in the past they were VERY expensive, why?

THANKS,
Gary