On my 4430 I remove the sight glass to drain it.  Previously, I had to fill it through the vent tube which was slow and messy.  This year, per the dealers recommendations, I installed a 3/4" close nipple in place of the sight glass, then I put a 3/4" cross on there with a plug on the top and bottom, and then the sight glass on the end.  This way I can drain it easily with the bottom plug, and it is much easier to fill it with a small container with a squirt nozzle from the top plug because it can breathe.