Haven't had to deal with plug in water heater tank in a while as we have On Demand water heater, but had 11 years experience with plastic plugs. I learned there are two different plugs! The threads are the same but one is tapered to make it easier to get started and the other - newer? - is straight and I found it a bear to get started which meant I was less likely to take it out and redo the teflon tape when it started to drip. Eventually I found a supply of the tapered plugs that lasted me until we sold the coach. needed one or two every year.
