do you mean the drain valve, to drain the water?
If so, those have 3 rubber 0 rings in them. They get old and dry. When you move the drain lever it drains all the fuel out. Then when you turn it off, it leaks. Is this what you are referring too?
If so you need tork bit sockets, I believe a t15 or t17 on a 1/4 drive ratchet handle. Theres 4 screws that hold the drain valve in place.
get the o rings from
Replacement O-rings for Ford Diesel Engines
they are cheap, he ships fast. You can also if in a jam use a piece of inner tube between the valve and the bowl. That seals it so nothing leaks. But it wont allow the drain to work. I have one this when the parts were not on hand and i wanted it to not leak.