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Dirt and moisture are the main causes of corroded tanks. Store your tank in a shed, closet, or a similar safe area. Improper storage is likely to taint any air left in the tank and rust the insides.. Try to keep the tank around room temperature, especially if you left air in it. Cold temperatures can lead to rust. Store the tank separately from other gases, oil, lighter fluid, and similar materials. Leave the tank uncovered in the storage area. In case of a leak, the tank could cause a fire around flammable materials. It can also explode if the pressure builds up too much. For these reasons, keep the tank away from children and animals. This is to prevent the tank from breaking down or reaching unsafe pressures over time. Look for a small ring on the brass fitting you use to fill the tank. To release the air, pull the ring back until you hear the air hissing out. Wait for it to stop. For safety, it’s best to drain the tank if you won’t use it for 2 or 3 months. If you still wish to store a tank that has air in it, keep it in a temperature-controlled room. Make sure the tank is empty before you do this. Then, twist the air hose valve off the tank’s brass fitting and set it aside. Flip the tank over, letting the excess moisture drain out of the fitting. When you’re finished, replace the parts and store the tank in a safe spot.  Some tanks have a drainage valve on the bottom end you can unscrew to easily drain out the moisture. Moisture can lead to tank corrosion, so frequent draining helps your tank last longer. Drain it after each use if possible.

Summary:
Store the tank in a clean, dry area. Set the tank away from flammable materials. Let the air out before storing the tank long-term. Tip the empty tank over to drain moisture.