1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 14Get this manual
MAINTENANCE
Bigfoot Models
Flush the internal water passages of the outboard with fresh water after each use in salt, polluted or muddy waterThis will help prevent buildup of deposits from clogging the internal water passagesUse Quicksilver accessory (or equivalent) flushing attachment
WARNING
To avoid possible injury when flushing, remove the propellerRefer to Propeller Replacement1Remove propeller (refer to Section 1C Propeller "RemovalInstallation")Install the flushing attachment so the rubber cups fit tightly over the cooling water intake holes