Brass Water Heater Plug
I have an Atwood water heater (and it's likely that you do too). I've been fighting it for years. Whenever I take the plug out to drain it and put in a new one, it leaks, even though I've always used the official Atwood plastic plugs. I got tip from another RVer to try backing off the plug slightly and re-tightening it, but it almost never worked.
I tried pipe dope and Teflon tape, but that never worked either. On occasion, I've spent over an hour trying to get the thing to stop dripping.
For the last couple of years, I put a black rubber O-ring around the plug and screwed it all the way in, but it made me nervous to tighten it that far.
Finally, on the advice of another long-time RVer, I went out and bought a 1/2" NPT Brass plug like the one shown above. I put some Teflon tape on it (though it probably wasn't necessary), put it in finger-tight, and used a wrench to turn it about a quarter turn more. It hasn't dripped a bit since I put it in.
I bought a square-head plug from Ace Hardware (a 17mm socket fits it perfectly), but I think the one above would be a little easier to use and should fit perfectly. My hardware guy at Ace Hardware suggested that if the thing ever leaks, to put some Dap Kwik Seal Caulk on it before screwing it in. This isn't the best caulk for your tub, but it will seal the plug for you and it will still be removable. I haven't tried this, (and may never need to), but it makes sense.
Don't be tempted to get the drain plug with a valve in it. It seems like a great idea, but they tend to leak (and sometimes break), and even if they don't, the inside diameter of the valve is miniscule. It takes forever to drain the tank, and you'll have to remove the whole thing to flush the tank with the wand — defeating the purpose of the valve.
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— Bob Ray