I have a Gravely Pro-Turn 52 with the Hydro-Gear ZT3200 transmission which is due for an hydraulic oil change. The instructions calls for 20W-50 oil which drains v slowly and may require a pump to void most of the old oil. Also, the instructions with drawing, id's the drain plug (in upper top of transmission housing) as an inlet port and a drain port which doesn't make much sense - one would think that a drain port would be located in a low part of the housing. This (inlet) port is actually connected to a hose that leads to a small holding reservoir below the seat (not mentioned in the instructions). I'm guessing that the oil will drain through the removed filter connection and vent from the removed reservoir cap and refill through the reservoir. The Hydro-Gear ZT models are all somewhat similar, so I'm sure some of you have been through the procedure. Can someone give me some tips on the process and any problems that they might have experienced ? The purge procedure instructions seems specific and straight forward and I have no questions there.