Plumbing question

[Braysgrandpa]

Beneath the bathroom sink of a 2018 Montana High Country 340BH. I know the red and blue ones are hot and cold PEX, but what are the white ones? Are they (he asked hopefully) central plumbing lines for installing an on board water softener or filtration system? Or are the they just some other unnecessary bit of hardware installed by the factory to confuse and befuddled me? Sorry it's sideways.

[JRTJH]

"Central plumbing lines for installation of an onboard water softener" ???

You certainly are wishfully dreaming.... Those are the two lines that connect the "black tank flush fitting" on the side of the trailer/in the convenience center with the anti-siphon valve (located at the top of the two white lines) with the spray nozzle that's located in the side of the black tank. If you get on your hands and knees with a flash light, stick your head inside the vanity and look up, you'll find a "black square thingy with a flat top" (looks like this photo, but with white PEX tubing rather than blue PEX tubing). That "thingy" is the anti-siphon valve, notoriously famous for leaking, flooding the vanity and almost always at the most inopportune times.....

[NH_Bulldog]

Agreed; black tank flush plumbing.

[bobbecky]

You should feel very blessed that the air gap valve is where it is located on your rig. It could be located between the shower and the back of the pantry cabinet like on our rig. This photo was taken looking through the gap where the pocket door is located at the top of the steps going into the bath area on our rig.