Atwood uses a 1/2" NYLON Plug. Has tapered threads so it tightens when installed
Use a 6 point socket and tighten it just a little bit........head can snap off on plugs that are OLD. 15/16" or 7/8" socket---depends on vintage/vendor
NEW ones come 2 to pack
Suburban uses a anode rod/drain plug. Tapered threads also.....teflon tape OK to help seal
3/4" drain .....6 point socket 1 1/6"
Now if T&P Relief Valve is dripping (weeping) it is most likely due to loss of Air Pocket.
Air Pocket is by design in top of tanks
Air can be compressed...water can NOT
Water 'Swells' when heated.......no air pocket to control pressure increases the T&P will leak
Over time Air Pocket can be absorbed into the water
*Turn water supply OFF
*Open faucet hotside to relive pressure---leave open
*Pop T&P Open via lever.....let it Snap Closed WHEN water stops running out
*Open water supply
**CAUTION: When popping T&P Open water may be HOT