There are several ways of identifying a leaking tank or cylinder:

Smell. This is why the odorant is placed in the product. If you smell the unmistakable odor, there could be a leak or open fitting somewhere in your LP-system.

Oily film around the valve or fitting connections: small leaks often leave an oily residue at the point of leakage.

Sound. A more severe leak will sometimes emit a sound from a low “psssss” to a high pitch squeal.

Fuel level decreasing faster than normal. If the level of propane is dropping faster than normal, one possible scenario could be that a leak exists somewhere on the container, it’s lines or the apparatus that is being used.

Leaks in liquid space will usually cause a frosting or freezing around the leaking spot.

Once a leak is suspected or if you just want to routinely check for leaks, a liquid leak detector or gas sniffing device is recommended. For emergency detection, soapsuds can be used. The liquid detector or soapsuds will cause a bubbling up effect that will point out the leaks origin. However, continued use of certain brands of soap could cause corrosion to the brass, rubber, or sealant used on the tank valves or fittings.
If the leak is on the propane container, get it outside and away from any source of ignition. If the leak is on the fuel line (vapor or liquid), shut off the flow of fuel by closing the service valve. Once you have found a leak or suspect one, call your propane supplier. They will guide you through the situation.