Propane tank exchange at Petro-Canada.

Propane tank exchange – If you have a 16 lb empty propane tank, you can quickly and conveniently exchange your approved tank for a full, certified propane tank at Petro-Canada™ gas stations.
Buy a tank and tank disposal – If your tank is obsolete or damaged, you can start fresh with a new approved propane tank at Petro-Canada gas stations, and leave your old tank behind for disposal, no charge.

How to tell if a propane tank is empty.

Here are a couple of tips to figure out if your propane tank is empty (or almost empty).

Attach a heat-sensitive gauge to the side of the tank. Pour hot water on the gauge. A colour gauge will indicate the amount of propane left in the tank.
Look at the metal ring on the top of the tank. There are letters and numbers stamped into the metal. Look for "TW" followed by a number. This is the empty weight of the tank. A propane tank generally weighs about 18 to 20 lbs. Put the tank on a scale and if it’s heavier than the TW number, the extra weight is propane still in the tank.