Im trying to install a bulkhead on the bottom portion of a 55 gal drum. I have a sch 80 bulkhead and i put the gasket on the inside. After i hand tightened it i gave it an extra 1/2 turn with my wrench but im still getting a leak. After alittle more tightening it still continues to leak. What am i missing here? Do i need to use silicone or something else?