On Fri, 12 Nov 2010 18:24:20 -0500, Gene
wrote:

Forgo the "Y" valve for an appropriately rated "T" and 2 proper
valves?

Yes. All you need is a T and one ball valve, assuming you already
have a seacock on the raw water through hull. My old boat was set up
that way and it worked fine. Alternatively you can just close the
seacock and pour antifreeze into the top of the raw water strainer
while the engine is running.