Draining the oil thru a hole in the bottom of the tranny while it's hot is obviously going to enable one to get more of the old oil out verses trying to put a line down in it to pump the fluid out.
Many of the commercial mowers have a spin on oil filter that can be removed to drain the oil but even on those it would be better to have a drain hole down at the bottom so all the old oil can be drained.
I bought my mower in June of 2020 and it was not equipped with an hour counter so I have no way of knowing how many hours it had on it before the original oil in the trannys became degraded. I just use it to mow my lawn and it's not used for commercial purposes.
Yeah, I'm aware that draining the oil doesn't change or clean the oil filter. On mine the filter is internal and one would have to disassemble the entire tranny do get to the filter. Changing the fluid will work just fine tho, similar to how many late model cars do not have a way to change the internal filter which is probably just a screen.
My tranny is not failing at all. If functions perfectly. The problem was the original oil was degraded and when the trannys got up to operating temp, the fluid was so bad the tranny was not functioning properly due to the bad fluid. This is common on these types of trannys.
After changing the fluid, it performed perfectly for the 1.5 hours it takes to mow my yard and the trannys were very quiet and were very responsive so there is no problem with the trannys at all now that I have drained the old oil and put in Amsoil 20W-50 Synthetic Hydrostatic Transmission Fluid
So, I'll be getting many more years of good performance out of this mower like I do my cars and trucks running full synthetic lubricants.
I'll swing by here in a few years and provide a updates about how change the tranny oil each year and how the mower is still running like new!