There is no drain plug in most oil systems. I use a siphon tube about the size of a grease gun to remove oil when I need to. You can disconnect the outlet hose to the oil pump and drain that way, but it takes a long time. If you get any air in the lines, make sure to get rid of all the air from the system. Air bubbles in the oil pump can keep the pump from lubricating the engine.
Any time I mess with the oil lines or pump, the next tank of fuel, I put some oil into the gas in the tank to make sure the pump is going to be working properly. Overoiling for a tank of fuel may foul a plug or two, but under-oiling can squeak a piston in 4.5 miles. Been there. I hate that sound.
take a pump out of a 90w bottle (clean it first of course)
or a pump out of a gallon hand cleaner bottle , just leave the small amount in the bottom of the reservoiur , so you dont get a bubble in it and ruin your engine .
fill it up with fresh good quality 2 cycle SNOWMOBILE oil ! your good to go !