If you invert a Tohatsu/Nissan (or any other brand) 4-stroke OB, you will spill crankcase oil where you don't want it. No problem with a 2-stroke, as there isn't any crankcase oil.
LU lube will stay in the LU for either a 2- or 4- stroke, as it is sealed.
It's only a couple of 6mm bolts to pull the tank off to flush it, BTW. Of course on the M3.5 2-stroke, there are a bunch of screws to remove to get the cowling off to access the fuel tank.
How I did it : remove the pipe from the output of the cut-off valve, and then place the output of the valve over a receptacle - open the valve and the fuel pours out. Let it all drain out then add a little more gas to the tank to flush it.
Unless your a magician like me, yes....Actually anyone can do it from underneath if they are careful and don't mind scraped fingers. Sometimes the screws weld and it would take longer than the typical 30 seconds to remove it, that's when it's time for Bloody Fingers 101.