In reading the replies, I wondered if there is a type of water soluble
lubricant (similar to that used in marine toilets) that could be poured into
thru hull drains with valve closed. Then by opening and closing valve
several times quickly while draining, the lubricant would coat valve
internals as it passes through. May be better than nothing until the boat is
hauled.

'Twould be next to worthless, Graham...just as they are in toilets. You
don't want a thin lubricant, you want a thick one that resists
dissolving in water, even if it is technically considered water soluble.
That's why teflon grease is the lubricant of choice in submersable pumps
and used by marine toilet mfrs...it lasts a while.

Peggie
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Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://www.seaworthy.com/html/get_ri...oat_odors.html