Propane tanks

If one tank one wont empty out easily perhaps your tank selectors automatic switch over doesn't work right. (You do have to keep both tanks fully open for it to work.)

There will always be a little left in the tank. The cutover valve senses the pressure drop JUST BEFORE the tank goes empty and switches to the full tank.

If the first tank were allowed to go completely dry, such things as pilot lights would go out and/or air would be picked up in the system which might cause misfire on the HW or heater.

I have 2 propane 'cylinders' (tanks are permanently mounted) with an auto changeover regulator.

I NEVER have both valved in.....just the way I do it.

In service tank will empty cause when I go fill it it takes 7.2 to 7.5 gallons to refill. (30# cylinder---4.2#/gallon)

I personally think dealership is blowing smoke and has given you a 'band-aid' fix for a faulty regulator.
How 'not empty' are your cylinders when you refill?

I keep both open and the "empty" one takes 7.1 to 7.2 every time.

faulty regulator, that's the problem for sure

Tdmeme wrote:
Purchased a new fifth wheel 2 months ago been in the shop for numerous things, they are telling me to leave propane tanks open for them to work correctly , the tanks don't empty out completely

What do mean "Don't empty out completely" takes 6.9 gals to fill or way less? If the regulator is set to the only open tank it should take 7.0, if the filling equipment is working correctly.
I leave both open and always get 7.0+ in the empty tank.

Fyi
The regulator switches over when the "in service" tank dropes below 10psi.
usally thats empty but in cases of hi demand you could draw the tank down below 10psi but still have a couple gallons left. once it warms back up you could use it out.