This location is right under the lathe chuck. Tangoromeo removed his chuck to drain the gearbox but I didn't. That's another story.
The tubing I had was undersized, but I just wrapped some paper towel around the end and it kept things from getting out of hand oily. One coke can holds all the oil from the gearbox and the engine cleaner I sprayed it out with...barely.
Gearbox door with mounting bolts and filler cap removed. You can still see the drain tube on the left side of the shot. You will also have to loosen the motor mounting bracket and remove it from the door (after draining) to get the thing off.
I thought the gearbox might drain more easily if I removed the filler plug to relieve any suction.
Yuck, this is before being sprayed out with engine de-greaser. I heard carb cleaner would strip the paint...not good. After my spray down there was even more gunk in the bottom. I tried washing it out the drain tube...which sort of worked, but a bigger tube would probably be better.
I spent a lot of time with a telescoping magnetic pickup after flushing the gears and wadding paper towels in to get the last bits of paint and steel chips. I let it dry overnight.
The gasket looked pretty bad...
...so I took the liberty to make a new one. Blue silicone was easier for me than making a gasket like Tangoromeo did. It even worked.
I forgot to take a picture but I used the same gear oil Tangoromeo recommended. Mobile Spindle Oil Medium #10
I bought a condiment bottle from True Value to use to fill the gearbox. Be careful, it doesn't take much.
Also be sure to check the oil level every time you run the machine. I had an imperceptible leak from one of the 3 bolts above the drain plug.