1979 4HP Merc mentenaince

[Lau.tm]

Hi everyone,
I do maintenance for my old Mariner 40 (4 HP, 2T) and I find this screw under bottom cowl. It look like the oil screw from propeller gear housing but when I opened it is dry inside.
Can anyone tell me if i had to put oil inside or is something else.

 

[Texas Prowler]

Well it's a two stroke so likely just a drain for water. If your water impeller is working you should see water shooting out of that hole with the outboard running.