"Bulkhead fittings are commonly used with our cone tanks for installing fittings into the bottom cone (non-full drain tanks) tops for filling and even sides for special purposes. Bulkheads attach to the tank walls by drilling a hole of appropriate size into the tank, then threading a piece of the bulkhead on one side and another piece on the other side and threading them together. Attached to these pieces are NPT female fittings for threading pipes into. The threads for the bulkhead attachments are reverse thread, so when the NPT pipes are put into the bulkhead, there is no chance of loosening the bulkhead fitting from the tank since the reverse threads will only get tighter if a lot of force is applied. Inbetween the bulkhead pieces is a plastic (chemical resistant) gasket and then a rubber gasket on the other side. The common gasket for the bulkhead fittings is an NBR gasket. This material is good for general purposes such as with water and mild chemicals. When it comes to more corrosive applications such as biodiesel, a viton gasket is required."