Mercury 300 XS OptiMax Manual page 130

OUTBOARD INSTALLATION
HOSE AND TUBING CONNECTIONS
Fuel Hose
The minimum fuel line inside diameter (I.D.) is 8 mm (5/16 in.), with a separate
fuel line/fuel tank pickup for each engine.
Fasten the remote fuel hose to the fitting with a hose clamp.
Oil Hoses
Connect the remote oil hoses to the engine hose connections. Fasten hose
connections with cable ties.
Water Pressure and Speedometer Hose or Tubing
NOTE: This applies to models without SmartCraft gauges.
This outboard has a speedometer water pickup located in the leading edge of
the gearcase. If you want to use this water pickup for the speedometer,
disconnect the water pickup tubing from the speedometer sensor and route
tubing out of the cowl. Install the coupler provided with the outboard on the end
of the tubing.
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