1988-1992 Mercury Force 5HP Outboards Service Manual, Page 14Get this manual
ACLEANING FUEL TANK 1Drain and flush fuel tank once year with fresh gasoline or solvent
NOTE: Flush more often, if required
BINSPECTING FUEL TANK CAP (1988A)
123Inspect cap gasket (A) for signs of cracking and replace, if necessaryInspect retaining ring (8) and anchor (C) for damage and replace, if necessaryInspect fuel cap (D) for cracks and replace, if necessary