I always just used plain old electrical wire nuts, screwed onto the end of caulk tubes to seal them. I would squirt just a dab of the caulk into the bottom of the nut, and screw it on the tube nozzle, giving an air tight seal.
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2011 Flagstaff 831 RLBSS
A 72 hour hold in a psych unit is beginning to intrigue me as a potential vacation opportunity.