Gene,
On our 2004 3295 that check valve is right under the bathroom sink. Our towels were soaked!
We found that the Calgon REALLY helped, it soaks off stuff, specially minerals.
I had mineral deposits showing in the toilet, nasty little ring, NOTHING would take it off. So, I put some Calgon in there, enough to cover said nasty little ring. Days later, ring gone. Course, we were NOT inhabiting Tana at that time, so, it could soak real good.