I heard that Blue Rhino was in some sort of suit over not filling tanks to the proper level. A 20# bbq tank holds 4.7 gal. The new OPC valves are designed to shut off gas when the bottle is full. The valves have a little float that shuts off the gas when the tank is full. The float length on a 20# bottle is 4inches long and on a 30#bottle it is 4.7 inches long. If you placed a 30lb valve in a 20lb tank, your fill would be reduced by about 3/4in. The 20lb bottle I had filled yesterday held 4.5gal of gas and that is where the valve shut off the pump. Since the tank didnt hold 4.7 gal, did I get shorted, no I paid for 4.5 gal of propane. My tank could easily of had .2 gal of gas left in it, but I got what I paid for. Those tanks you swap out at the corner store always seemed skeptical to me. Simply picking one up some seemed like they where heavier than others. If they all had the correct valves, and where filled properly, they should all have the same amount of gas. That doesnt mean they will all weigh the same and all of the bottles should have their empty weight stamped on them somewhere. When getting a bottle out of one of those exchange places, you are getting used tanks made by many different manufacturers. They are all supposed to be inspected and filled before going back out to be exchanged.I like having my personal tanks filled where I pay for what I get rather than rely on some unseen person at a refill center that does nothing but refill tanks all day long. Only thing about those exchange places are they are easy to find when you need a tank, but if I need gas and where I usually buy it is closed, I can always just swap my tank at the corner store, no questioned asked.
My two 30# bottles I have decided to recycle into something more useful. (thinking a forge),After checking, it seems recertifications are only good for 5 years, not the 12 years of a new bottle. It was going to cost me $26 +tax each to have the valves replaced and recertified which means in 10 years I would spend $52+tax each in recert fees. The new tanks are $58 and good for 12 years. Not much difference in total cost or savings.