My wife and I just became the proud owners of a 1987 Catalina 34 tall rig. She is in beautiful condition, however, the previous owner seldom used the water tanks. I have filled and drained the aft and starboard tanks several times and am ready to sanitize them. I have also removed the 4" clean-out on the starboard tank and removed whatever was used previously to seal it. I have read on the forum that I need to use a non-hardening thread sealer but I can't find a reference to a specific brand(s). One of the sailors on our dock suggested Vaseline petroleum jelly but that seems way too easy! Any suggestions/tips would be greatly appreciated.