I did mine today. What a pain in the @#$! getting the plastic plug back in the water tank.
I also must say, I am not hip on one cup of bleach directions. I like 4 cups, then after flushing and sitting for 30 minutes, flush with a gallon of white vinegar in the holding tank to deactivate the bleach, and sweeten the tank.
When I bought the RV, I don't think the dealer sanitized the tank. The water was always nasty in the lines, even when using city water. After this, everything from the holding tank, to the city hookup tastes like house water from the spigot.