In the Alpine 3640, the vacuum/check valve is inside the wall between the "toilet closet" and the bedroom. Inside the toilet closet, there is a shallow linen cabinet on that wall. I have searched high and low in that cabinet trying to find an access panel to at least see that valve. Nothing. Unless I cut a hole in the cabinet, and then mount my own access panel
. Now, on the bedroom side, SURPRISE! There is a 120VAC duplex socket in that wall . . . below the valve if indeed the valve is at least 6" higher than the top of the toilet.
So, let's add it up here . . . coming up from the basement . . . The Iota 50 Amp Transfer Switch . . . a 120VAC 15 amp breaker Duplex Socket . . . some RG-6 TV coax running about . . . and at the highest point, a Plastic Vacuum/Check Valve! Hmm, maybe I ought to start using WD-40 for flushing the black tank?
Hank, you are absolutely correct in pointing out the "change of design". As you can see in the diagram, not much of anywhere to relocate and still have it higher than the toilet. I have found a SharkBite spring loaded 1/2" check valve rated for 120 pounds pressure and for use on Pex. I'm thinking that this might be a "change of design" to "over-design". 120 pounds pressure is about 8 atmospheres, which translates into a fresh water column some 265 feet high! Surely that is better than six inches above the toilet lid.
And, the spring keeps the valve closed when pressure (water) is not applied from the outside, thus trapping any gases inside the Pex piping. In theory, ought to work.
Ron