This year, for the first time, I had some leakage through the skimmer--I'll just replace the "tupperware" cover for next year. I always prefer the screw-in plugs to the expanding rubber corks, but my dad used them pretty effectively for years. With the screw-ins, be sure to use teflon lube on the gasket and while they should be wrench-tight snug, don't play gorilla on them or the gaskets will be squeezed out.