You need to sanitize the water system with bleach followed by vinegar. A few years ago I had a similiar problem when I filled the fresh water tank and HW heater with well water at my house. Minerals and gases that are trapped in the water due to high pressure at the bottom of the well, when pumped directly to the RV tank and then heated in the HW tank caused a slimy white growth plus smell. When I added an above ground storage tank, outgassing could occur since the water was no longer under pressure for a few days. Now I can fill the RV tanks from the above ground tank w/o problems.
Texas Baptist Men-Retiree Builders member since '01
13 Silverado 3500HD D/A, 2wd CCSB srw, custom RKI bed
11 Cruiser CF32MK