Mercury Force 9.9, 15HP Outboards Service Manual, Page 54Get this manual
CINSPECTING SCREENS AND TESTING CHECK VALVES1Remove screens (A) Remove them with sma ll pin or need le2Inspect and clean screens Replace if extremely dirty "
Test check valves
Place tube or hose over check valve (AI
NOTE: Be sure tube or hose is seated squarely on the cylinder drain cover surface so that there are no air leaks