What is a one-sentence summary of the following article?
Do not attempt to refill a compressed canister on your own. Take it to a filling station where a trained professional can fill it for you. Gas canisters can explode or leak if they are filled improperly.  If you are using a canister for diving, check out your local diving shop or school. These usually keep a technician on hand to refill diving cylinders. Look for hiking or nature shops near high altitude mountains if you need tanks for mountaineering. If you are using oxygen for home therapy, search for a company that delivers refilled oxygen tanks to your home. Schedule these deliveries on a weekly or monthly basis.  When you first start oxygen therapy, your doctor will likely suggest an oxygen company. If they do not, call them and ask for a referral. Some insurance companies may require you to use a certain oxygen provider. Call your insurance agent to learn what your options are. Not all compressed gas canisters can be filled more than once. These canisters can leak or explode if refilled. In these cases, buy a new canister of oxygen from an oxygen supplier instead of trying to refill it.  Look at the label on the top of the canister or in the manufacturer's manual to see if you can refill your canister or not. Refillable gas canisters will often be made of steel or aluminum. Their walls will be 1⁄4 inch (0.64 cm) thick or thicker.

Summary:
Take tanks for recreational activities to a filling station. Hire an oxygen company to deliver refills. Buy a new gas canister if yours cannot be refilled.