I believe the 'fresh water drain' valve probably is to allow air into the tank so that it drains quicker ...
'bypasses' are generally to bypass the use of this appliance, such as the water heater tank, so that your water is not going into, especially when you 'winterize' and don't want any of the 'pink stuff' winterizing liquid to fill the water heater tank, which is not needed.
there may also be a 'water tank' bypass, which just means that when you are on 'city water/pressurized water' from a spigot, it is not filling the tank, but just being used by you while in the coach
'14 Palazzo 33.3 bunkhouse 34' diesel
KingTailgater2 Dish HD, 100w/5a SOLAR, BlueOx
100,000+mi since '14 - US, Alaska, Canada.... formerly Georgia, then NorthCarolina, now Alabama : )