Cylinders used to recover refrigerant have to be specifically designed to be refilled. This is because refrigerants are pressurized and can be flammable or corrosive.
Recovery cylinders can only be used for one refrigerant. For example, if you use a recovery cylinder for R-410a, you can only recover R-410a with that tank. This is to prevent contamination or mixing of refrigerants.
All refillable containers for refrigerants must be hydrostatically tested every 5 years.
When filling a refillable container, you must take care to not fill beyond 80% capacity. This is because the refrigerant is pressurized.If the storage area gets too hot, the pressure inside the cylinder will increase and can cause an explosion. By leaving 20% capacity free, you are letting the refrigerant have wiggle room for that scenario.