It is tempting to say "Seek professional help" (You should be thinking of something other than what I'm about to punch line down below.)
First: as you move about the water changes.. This can lead to what I call..er.. After Effects (Also known as frequent flyer miles on the porcelain airline) or frequent use of the toilet.
So the old joke of the length of "Just a Minute" (Depends on which side of the door you are on). Consider a bath and a half floor plan. or 2 holes. NO waiting.
Now the Professional help.. IF you are buying used make friends with a good RV technician who can do a pre-purchase inspection... They may find that the rig looks good but .. there's about 10,000 worth of repairs needed (or more) and the deal is not nearly as good as it looks.
(See the seek professional help was not a joke.. Just not THAT profession).
