Atwood water heater drain plug tightening

Start by checking the threads on the tank. You can pick them clean with something soft like a toothpick. Vinegar also helps remove any scale. I bought new OEM nylon plugs but still need to wrap with 2 or 3 turns of thin thread tape. When my plug is tightened there are no exposed threads and little or no gap between the tank and the end of the plug.