There are no separate water runs in the RVs. There is NOT anyway to isolate the shower water inputs from the rest of the rig. Unlike newer houses there isnt a maniblock type setup for the water supply system. Basically these rigs are hand built one at a time. I really doubt there is a plumbing schematic anywhere, especially for a RV as old as the 2008 your describing. I have worked on mine for years, there pretty basic once the basement walls are taken down. You would see the hot(red) and cold(blue) pex supply runs which are 1/2 inch these days, and of course the drain pipes are all out in the open in a fifth wheels basement area. You could just call a plumber for your issue, its very basic set up in an RV.