If you DIY, you can install a drain plug kit on the pan to make this service easier the next time. Less fluid falls on your head when you need to pull the pan for cleaning and replace filter (if there is one).
With a plug, you can also do multiple changes (easily) to dillute as much old fluid as possible without draining the converter, which can be troublesome (or cause damage) in some cases. Not a complete flush, but better than a single change, since the converter holds the bulk of the fluid.
Manufacturers have gone away from providing drain plugs. Probably saves them 50 cents per unit...
(50 cents X 1,000,000 units= hey! bigger executive bonus!)
1986 300E 5-Speed 240k mi.