D5C losing power

I'm working on draining the fuel from my 1997 D5C XL, serial number 9DL00379. I think I've located the drain valve, but I'm not sure what size tool I need to loosen it.

Usually it's a 1/2 drive tap plug. Give it a tap with a hammer before you try to loosen it, then you'll need a pipe nipple in a hose to screw into the drain to open the ecology drain.

Take out plug #20, then screw a 1" pipe nipple onto a length of hose and fit it into fitting #18 to open drain valve #15.

I'm not clear on what you mean by hose length.

We made a setup with about 3 or 4 feet of heater hose, a pipe nipple that fit inside the hose, and adapters to connect the nipple to the drain plug. If you just screw a nipple straight into the drain it gets messy and you end up covered in fuel. This way's a lot cleaner and easier to catch the old fuel too.