Tohatsu 4 Stroke MFS 2/2.5/3.5A Outboards Service Manual, Page 45Get this manual
Maintenance 9) Replacement of Gear Oil
12Set outboard motor verticalPlace drain oil pan below oil plug 1, remove lower oil plug and then upper oil plug to drain oilRemove lower oil plug first when draining
Check gear oil for presence of metal particles, change of color (abnormal if clouded), and viscosityCheck lower unit internal components if necessary3Gasket
Do not reuseFill with gear oil (from oil tube or pump) through lower plug hole until gear oil starts to flow from upper oil plug hole without air bubblesOIL