If engine has fuel pump mounted on the engine then it is leaking gas into crankcase.
You can stop a leaking gas tank, by making a paste of soap on the hole of the gas tank.
Take it to a trained technician
take it to a mechanic, a gas leak is nothing you want to mess with.
If your vehicle is leaking fumes, then your gas tank needs to be fixed.
Carburetor needle valve probably leaking while engine is not running causing gas to run down the cylinders into the crankcase.
By calling a licensed master plumber / licensed gas fitter / Gas supplier
Not knowing what vehicle and engine you have you may have a faulty fuel pump leaking gasoline into the engine crankcase.
Look at the oil on the dipstick. If you have antifreeze leaking into the crankcase the oil will be milky.
Replace it.
If leaking from the rail itself, the rail will need replaced. If leaking from a seal at the rail, replace the rail.
It runs down past the piston rings. It may be a misfire or leaking injector.It runs down past the piston rings. It may be a misfire or leaking injector.