If formed in the gas tank hole is small and you do not intend to pour gasoline, then the first thing to stop flowing. Easier and faster all it can be done, carefully smeared the hole with bar soap. Next you need to gently remove excess soap using a cleaner. Be careful, because if you remove too much soap, the leak reopens. Degrease the surface. As degreasers you can use acetone or any other solvent. The degreased surface should be cleaned with emery paper and then leave to dry. Next you need to carefully cover up the hole cold welding and wait 10-15 minutes until the weld will not harden completely. Then soak a few rags with epoxy glue and carefully attach to the surface of the fuel tank by closing the flow. Wait 24 hours and then can re-use the machine.
Another way is suitable if the hole is comparatively large. Drain the gas tank of all gasoline, degrease, clean with sandpaper and dry the surface formed near the gas tank hole. Take some rags and soak them with glue. When the glue dries a bit, glue the cloth to the surface of the fuel tank by closing the flow and wait until the glue dries completely. Then apply two layers of glue on the cloth (the thickness of each layer should be about 1-2 cm). Thoroughly cover the patch of nitro and wait for it to dry. Then you can re-fill the petrol tank: a leak is likely to be eliminated.
If you don't have time to prepare the surface of the tank (cleaning, degreasing, etc.) – cut from paronite washer, then install in the formed in the tank hole screw and washer, and then cover the surface of the fuel tank paint. Perhaps the hole will first have to increase in order to close it with the screw, but the leak will be immediately eliminated.