No drain plug. Unit must be removed, item 8 (sealing cap) and 6 (filter) removed, and turned upside down and drain thru the hole. Also I would recommend changing the main oil filter (item 21) while the unit is upside down as there are a few captive items that will fall out otherwise when you remove the oil pan (lower case). one is item 20. Item 8 should also be replaced as they will age and crack leading to water intrusion.
Also 1686788SM is the current replacement for the 1693528 mower.
1720092 (superseded to 1720092SM) is a K56A-8MP
1717194 (superseded to 1686788SM) is a K56A-SMP
1717194 was just a newer version of the K56A. Per the above IPL image all K56A are the same unit internally. It just some of the internal parts have been upgraded.
Just be aware this is a $2000+ transaxle. Comes with pulley kit but may not come with the fan.