My first motorhome did not have factory installed by-pass valves ... the original owner installed
three valves and a true "by-pass pipe" which (if the valves were opened and closed correctly) would allow the water to by-pass the hot water heater and allow no water into or out of the hot water heater OR if turned opposite required the water to flow through the hot water heater ...
My two Winnebago motorhomes have only had
one by-pass valve ... it really only cuts off the flow of water into the input pipe of the hot water heater ... and instead diverts the flow to the output piping of the hot water heater ....
You will notice that the hot water heater is pressurized even if you have the by-pass valve set to "by-pass" ... soooo ... make sure that you use the pressure relief valve to release the pressure in the hot water heater before you attempt to drain it ...
I remember very clearly the <span class="ev_code_RED">BIG SURPRISE</span> I got the first time I removed the drain plug from a hot water heater on a Winnebago motorhome when I was de-winterizing at a campground in Arkansas