Lynnmor-
Apparently, part of the manufacturing process for Atwood (now Dometic) aluminum water heater tanks is suspending the laws of physics inside them. According to the interweb experts, they are the only aluminum vessels on earth that will NOT react and corrode in the presence of water. Buy an aluminum boat, it will have an anode. An aluminum fresh water storage tank, it needs an anode.
In reality, Atwood/Dometic makes no claims that the cladding in their tanks will prevent corrosion. In fact, they acknowledge that the cladding is the sacrificial anode, and that in the presence of certain types of water, corrosion can happen very quickly, and pinholes can form in the tank. Or at least they did before the company was acquired by Dometic. Their documentation is completely different now.
It’s also not true that your warranty will be void if you use anything other than the plastic (oops, nylon) plug. The actual wording in their warranty document is: “damage or failure caused by installation of accessories not manufactured and marketed by the Seller or any non-Dometic parts that are installed as replacement parts”. The key words are “damage or failure caused by”. That’s a pretty standard position for a manufacturer to take regarding warranty coverage.
The warranty on water heaters is two years, so the smart thing to do would be to use the recommended plug during the warranty period, then do what you want after that. Unless you’re spending long periods of time in an area with sub-par water, your WH will most likely last much longer than that. Mine’s nearly 20 years old, and other than the original plug, it’s always had something other than the nylon plug in the drain hole. The brass petcock that’s in it now has been there for several years, and I’ve removed it periodically to flush the tank.
I’ve also used an anode rod, and as long as it’s more anodic than the tank cladding, then the rod will corrode rather than the tank. That’s just how it works. I use either thread tape or Rectorseal on the threads. It doesn’t leak, and the threads are fine.
If you do happen to damage the threads (which can happen even with the nylon plug), provided it’s not too bad there is such a thing as an NPT tap or thread chaser.
:):)