How do you replace windshield washer tank and pump on a 1991 Nissan hardbody?

you might not need to replace it it may just be clogged.

on my 96 four cylinder the tank is held in by three hex-screw bolts. remove the tank and notice the only two things still connected are the tube for the fluid and the wires, both are connected to the pump, the tube and pump can just be pulled out. get a flat head screw driver and pry open the bottom cover of the pump (that cap looking thing that the tube connects to) you will probably see a bunch of blue gunk, go ahead and clean all that crap off, spin the wheel a couple of times. turn the truck to "ON" and pull the wiper fluid lever, if the wheel doesnt spin, go get a new one. if it does you need to glue back on the cap, BE CAREFUL not to press the cap back on too hard because you may wedge the cap onto the wheel, not allowing it to spin, also not to get glue on the inside where the wheel spins cause you may just glue the wheel!

make sure the tubes are free of gunk, you should have two check valves, one for each nozzle, right before each one on the nozzles, note the arrow direction after cleaning when replacing