[terry and jo]

My "aid to determining" LPG levels is a bit different and calls for a discerning ear.

When handled, the sound of an empty tank (especially a 40# bottle) has a different "ring" to it than what a full one does. If uncertain as to the level of LPG in the bottle one can tap the bottle beginning at the top and working down in something like 1" increments until one hears the different sound given when LPG is at that level.

Motor31's solutions is the best, easiest on the knuckles, and much more accurate method of determining the level. Much better than the "tap and listen" method. But, if warm or hot water isn't necessarily available, the tap and listen will do in a pinch.

If there is no discernable difference in sound by tapping down the side, then I take a screwdriver and loosen the bleeder screw on the side of the valve to judge how much pressure is escaping. To verify that the pressure escaping is definitely less, I also loosen the bleeder screw on the tank that seems to be the fullest to see which tank allows vapor to escape the fastest.

Of course, it is important to make sure the bottles are out of the compartment when loosening the bleeder screw.

Terry