Ask a Tohatsu agent.... but I would have thought it is outboard engine gear box/leg oil. Don't know the Tohatsu but you normally fill the thing from the bottom hole until it comes out the top on an outboard so you need a squeezable bottle with a pipe fitting or a little pump....can be bought at most swindleries.
SAE 90 ie gearbox oil-lot thicker than engine oil. Can get it from Halfords, many garages. Just changed mine-screws were very tight & as Howardp says you have to pump it in the bottom until it comes out the top-need a small flexible pipe to fit in the bottom hole-the one that comes as standard with most bottles of gearbox oil is too big. I had to loosen the screws with light taps with a hammer on a large screwdriver-guess animpact driver would do as well . Hope this is of help