I had to pull this to get to the charcoal cannister, so I decided to clean it.
Cleaning the outside was easy. The inside was tricky. After disassembling the thing (which basically amounts to removing the pump), I put about a cup of rock salt and some water in the tank and shook it around for about 10 minutes. That did OK so I dumped that and repeated. That got 90% of the black crud from inside the tank.
To reattach the pump to the tank you have to install a nut inside the tank. Luckily you can do this by reaching a wrench into the fill hole on the top of the tank. Here's the rough procedure:
1) Drop the plastic washer into the tank and giggle the tank around until the washer sits over the small hole where the pump will go. This is the most difficult part of the procedure.
2) Line the washer up so it's exactly over the hole. Use a screwdriver to move it around if needed. If you had forceps or long pliers, you could use those to position the washer instead.
3) Carefully put the threaded part of the pump into the hole, being careful not to disturb the washer.
4) Hold tank sideways, being careful not to let the washer drop off the pump.
5) Using a large/deep socket (1", I think) on a long extension, manuever the plastic nut/filter piece into the tank and screw it onto the pump assembly.
6) Tighten to whatever torque Mike Romain specifies
I took me about 5 tries to get it back together.
I tested the pump motor on a 12v power source and it seemed to hum along OK. I can't really see using windshield washer in the CJ, so won't be refilling the thing any time soon.