I use the a gizmo screwed into the skimmer pipe fitting and use teflon pipe tape on the threads. I only rely on it as a plug to keep water out of the skimmer pipe. For ice expansion I pack the skimmer with eccofoam....a closed cell packing foam that is the same as the foam used for pool noodles. Reduces the bulk of water in the skimmer and allows plenty of 'soft' room for ice expansion. Once I blow out the skimmer line I fill it with RV antifreeze up to the pump inlet which is probably 14" above pool water. Thus, if the gizmo threads do leak, AF will go into the pool, not the other way around. Once in a while I check the AF level to make sure it isn't leaking.
Al