Mike, soda is commonly used to help remove the odor and taste of bleach following tank and system sterilization. It can serve anytime to help remove off-tastes inadvertently taken aboard the tank at some parks.
Mark, I don’t know about your model year, as it’s chronologically right between the coaches we’ve owned. On the ‘85, there were simple T valves accessed via holes in the floor under each fixture’s hot and cold lines. Our ‘06 Beaver has a manifold of “on/off” water valves in the water or wet bay, mostly a cold and a hot for each coach fixture; only two valves, hot and cold located at the bottom of the manifold, drain all water circuits there.
Joel