Gas tank leak repair at Canadian tire or replace it,replacement is the best choice if you're keeping the car.
take the tank off and flush it out with a water hose...
take it to the fix...
you can buy,a tank repair kit at any auto parts store, these kits are not expensive, and easy to use if you follow the directions
You can stop a leaking gas tank, by making a paste of soap on the hole of the gas tank.