I have the 169FML engine as well. It has a drain plug on the bottom
of the engine. Here's a couple pics. You can see how the hole in the
skidplate doesn't line up for draining.
On My 150 Maxfine the manual indicates the larger side bolt shown in your photo, that contains the screen, is the drain. I have been changing my oil through there. Is that not right? Seems like all the oil comes out just fine as the bike leans that way and it actually becomes about the lowest point.