Update:
Did the wintering yesterday and took along a new plug that I got at a local RV dealer.
Here's my conclusion. The difference seems to be with the Atwood OEM plug and the aftermarket plug. Atwood is the 15/16 and it's white nylon. The aftermarket is 7/8 and is black. When I bought them the dealer had the white Atwood in a twin pack for over 6 bucks. The black aftermarket was only a buck 49 each. I got 2 of the aftermarket and they seem better then the OEM and it was easier to use the 7/8th socket with a 8 inch extension bar. I did Teflon tape the new black plug and it fits great. The WH tank was full since July and never drained and the water looked great, no sediment.
Thanks for all the input I feel comfortable doing this job from now on with the Atwood.
On a side note after having a suburban for the past 2 TT's I kind of like the Atwood better. Biggest convenience is that the electric operation switch is inside the TT at the main control panel and the Suburban was always a switch inside the WH door that you had to nearly stand on your head to see.
The Suburban has a nice illuminated rocker switch that's easy to see if the WH is on electric and the LP switch is the same and has a separate DSI fault light. The Suburban LP switch inside the TT was confusing because it only had one light when you turned it on and then when the unit fired the light went out unless there was a fault with the DSI.
Thanks again I've expanded my RV knowledge and that's always good.