I was just wondering about this, so I got out the spare bathroom scale.
Put a drop of oil on the center stem threads and made sure both tank valves were closed.
Removed the center stem nut and both tank fittings.
Removed door side tank and weighed 37 lbs.
Removed sink side tank and weighed 27 lbs. I'd say +/- a pound or so.
Reinstalled tanks and tightened down center stem bar, making sure tank spacing was right for bar grooves to mesh.
Put valve main tank indicator green to door side tank and opened door side tank.
So, if I open the sink side tank valve, meaning both tank valves are open, and the door side empties from running the furnace at night, will the valve auto switch to the sink side tank?
Obvious I don't use much propane.