Call the retailer where you purchased your gas tank to ask about take back and recycling options.
Gas cylinders larger than one pound in size include helium, propane, oxygen, acetylene and MAPP tanks.
Do not throw tanks or cylinders in the trash, and do not attempt to puncture the cylinder.
Because gas cylinders and tanks contain a compressed gas, if they are thrown in the trash they can explode and cause injury to solid waste workers. Although a tank may seem empty, a small amount of explosive gas remains even when it no longer supports a flame.
Check with your retailer for options for gas cylinders like the 20-lb propane tanks you use in gas grills.