Your propane tanks must be the OPD (overfill protection device) style or you won't be able to get them refilled (legally.) The OPD tanks have a triangular knob on the valve. Older style is round.
Also, check your propane tanks for the manufacture date. It's a MM-YY format somewhere on the vertical "C" collar around the valve. If it's more than 12 years old, it must be re-certified before it can be refilled
Being 30 pounders, they are much more valuable than 20's. You can get them refitted with OPD valves and recertified for about the price of a new empty 20. If they are in good shape, they're worth the investment.
'12 F250 4x4 Super Duty PowerStroke 6.7 diesel
2011 to present: '11 Cougar 326MKS
1999 to 2011: '99 Sunline T-2453
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