GMC 1996 Sierra Owner's Manual page 282

Adding Washer Fluid
Open the cap labeled WASHER FLUID ONLY. Add
washer fluid until the tank is full.
NOTICE:
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When using concentrated washer fluid,
follow the manufacturer's instructions for
adding water.
Don't mix water with ready-to-use washer
fluid. Water can cause the solution to freeze
and damage your washer fluid tank and
other parts of the washer system. Also,
water doesn't clean as well as washer fluid.
Fill your washer fluid tank only
three-quarters full when it's
very
cold. This
allows for expansion, which could damage
the tank if it is completely full.
Don't use radiator antifreeze in your
windshield washer. It can damage your
washer system and paint.
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