If a propane distributor refills 500 gallon bulk tanks the have got to have the certification needed to renew small cylinder qualification.
If my cylinder remains rust free...
I had four 20 lb pots hot galvanized in Oakland California in 1986. When Dale Erb shot Quicksilver he shot the pots with the same seafoam green tie coat as he used to bond to the bus. Then the pots were shot with OSHA white (or minimum temperature gain).
What used to kill old fashioned valves was overfilling the pot. The OPD float shutoff system cannot be used down here because the butane dispensers cannot deal with the OPD filler valve design. Hence my pots could not be filled in the USA. Tough.
But the days of worrying about rust-out are through. These are Manchester 20 lb pots.
I change valves changed every seven years or so for drill. Mexican gas has a lot of methyl ethyl mercapatans (odorant) and a lot of refinery lube oil in it. Many empty pots gain FIVE POUNDS worth of this junk.
A quart of lacquer thinner, resting overnight dilutes the oil enough to flush. But I need to wear throw away clothes, and gloves, and googles. Dig a deep hole and bury the liquid far far away from any structure or popular area. The odor will attract insects, and rise fears of "gas leak".
I have seen both aluminum pots and stainless steel pots. They have a knee-wobbling price tag. I have yet to see a valve assembly that claims to be superior.