Lower Unit

I have a 1993 Yamaha 55 hp that I just purchased. It is in very good condition but I have been giving it a once over. My problem is, I can't figure out how to change the lower unit lube oil. There are only two screw plugs visible - one says "oil level" and the other says "wash." How do I do it? (And what is "wash" for???"

[boats.net]

Oil level is the top gear oil screw, wash is for fresh water flush hose. There is a drain screw at bottom of gear case in the front of gearcase.

Lower unit -

Thanks.

Now for stupid question #2: the drain hole in front of the gearcase is for lower unit oil (not the water flush, right?) If so, do I lube through the bottom hole like the outboards I am familiar with, or drain from the bottom and fill from the top?

While I am at it, the fresh water flush doesn't look too efficient, as it is so small. Should the engine be off while flushing it, or would there be enough water movement to run it?

Thanks again.

[boats.net]

Fill gearcase by pumping oil into bottom drain screw until oil comes out top level screw. The wash port is for flushing motor but cannot run engine with this flush method.