One bit of information that may be relevant...
Manchester makes tanks and they make what they "van style" tanks. I have a 5 gallon Manchester van style tank on my camper, and a while back I had to have the main fill valve replaced. The guys at the propane shop who did the work explained it to me like this:
A regular "RV style" tank has the fittings welded up high on the tank. The "van style" has the fittings welded low on the tank.
The problem with the low fittings, is they are all below the vapor line, so internally, there are tubes from the fittings which run up above the vapor line.
I'm not quite clear if all the fittings have these internal tubes, but the bleeder valve at least must have one, or else it would bleed liquid any time there is anything in the tank.
I assume that the fitting for the main outlet valve must also have a tube so that it draws vapor instead of liquid.