2005 Yamaha F90TR 90HP Outboards Factory Service Manual, Page 41Get this manual
Periodic checks and adjustments
4Insert gear oil tube or gear oil pump into the drain hole and slowly fill the gear oil until oil flows out of the check hole and no air bubbles are visible
Pressurevacuum tester: YB-35956-A 2Apply the specified pressure to check that the pressure is maintained in the lower unit for at least 10 seconds
CAUTION:
Do not over pressurize the lower unit, otherwise the oil seals can be damagedNOTE: Cover the check hole with rag when removing the tester from the lower unitLower unit holding pressure: 100 kPa (1.0 kgfcm2, 14.5 psi) 3If pressure drops below specification, check the drive shaft and propeller shaft oil seals for damage