Yamaha 30DMH Owner's Manual page 44

Operation
the optional chromium-plated water pump kit
(see page 10) if you use the outboard motor
in acidic water or water with a lot of sediment
in it, such as muddy or turbid (cloudy) water.
After operating in such water, flush the cool-
ing passages with fresh water to prevent cor-
rosion. Also rinse the outside of the outboard
motor with fresh water.
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