On my RV, the bypass valves are on the front side of the water heater. I have to pull a panel behind a cupboard below the oven to access it.
Essentially all the bypass valves do is to disconnect the hot water line from the hot water tank and connect it to the cold water line. This allows you to simultaneously blow both lines at once with an air compressor or filling with pink antifreeze when winterizing.
You can simply pour bleach into the water tank's fill tube, which should be on the side of the coach, possibly next to the city water inlet.
The only thing that works on a RV is the owner...