1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 115Get this manual
Fuel Tank MAINTENANCE
Fuel Tank Components
The inside of the fuel tank should be cleaned once each seasonDirt or water may have entered the fuel tank during refillingClean the tank by flushing with clean, lead-free gasoline or keroseneIf fuel restriction problem is encountered, the fuel filter on end of outlet tube may be obstructedRemove cover and inspect filter for varnish, dirt or depositsClean filter by rinsing in clean, lead-free gasoline or kerosene