My 98 has a separate pump for the rear washer co-located with the resevoir in the front passenger side of the engine compartment--have a friend listen for the pump as you actuate the rear washer--if no sound, pump is either dead or not getting power. Check obvious things like fuses and connectors first. If replacement is required, pull off the filler neck on the top of the tank. From the bottom, there are three bolts holding the tank in place. Mark where each rubber hose goes when you disconnect them to lower the tank. Once you have the tank lowered, you can pop out the old pump and replace. Fairly easy, but the pump wasn't cheap ($90 at the dealer). Might be worth a check with at your local salvage yard first.
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Scott - '98 V70 T5M