Mercury 25 EFI FourStroke User Manual page 107

Use a Mercury Precision or Quicksilver accessory (or equivalent)
flushing attachment.
IMPORTANT: The engine must be run during flushing in order to
open the thermostat and circulate water through the water
passages.
Rotating propellers can cause serious injury or death. Never
operate the boat out of the water with a propeller installed.
Before installing or removing a propeller, place the drive unit in
neutral and engage the lanyard stop switch to prevent the
engine from starting. Place a block of wood between the
propeller blade and the anti‑ventilation plate.
1. Remove propeller. Refer to Propeller Replacement. Install
the flushing attachment so the rubber cups fit tightly over the
cooling water intake.
Flushing Device
eng
MAINTENANCE
WARNING
!
9192
97
27256
91‑44357Q 2
Attaches to the water intakes;
provides a fresh water
connection when flushing the
cooling system or operating
the engine.