Somewhere on a portable HD I have this with pictures but...Can't find.
You need
An old clutch or break reservoir the white translucent plastic kind, we use Honda Cub variant.
I piece of short plastic tubing to fit on the reservoir
I piece of plastic or Future board about 6 inches square
Some tie wraps
Attached are 1000 word pictures?
The idea you fill the reservoir with your favourite oil and put the lid back on.
Clip the whole assembly to the swing arm.
Unscrew the top from the reservoir and walk the bike forward until all the oil has run out of the reservoir.