I have never used the drain plug on the bottom personally. You can get an oil pump kit that you stick in the filler or I usually run them low or out of fuel and lay them on their side to drain the oil out the filler hole.
I made the mistake of taking out the drain plug on my old Victa when I first got it, but I won't make that mistake again. It's difficult to get out, difficult to put back so it doesn't leak, and in between the two it makes a filthy mess of the blade plate. After one try that way, I switched to Joe's method: tip the mower.
