Howdy, I got one of these (24v is the model) Best of all class C's I have owned. (had four over the years.) The corners of the over cab section, below the windows are known to have sealing issues. Specifically the aluminum molding does not do a good job of holding the intersection of the sidwall and under wall together. Suggest you push on it with your finger to see if it is loose. I have repaired my (along with some delamination ) by removing the molding and sealing it with Proflex then putting eternabond over the corner and replacing the molding. PS. The bathroom sink drains into the black tank by design.