Prompted by several recent postings I am trying to remove and replace a leaking thru-hull fitting under the sink in my Oday 25. The thru-hull is brass and has a brass valve threaded on top of it. So far I have been unable to unthread the valve from the thru-hull. I don't what to break anything or get into a situation which is irreversable, so before proceeding with lots of brute force I'm looking for advice on how to free up the valve from the thru-hull. The boat is on a trailer so I can get at both the inside and outside.