I'm a bit late here, but I figured I'd answer just in case you or others were still wondering about the answer to this question! The most important factor when winterizing your pool is the pressure of the blower/compressor. Having a high CFM is good, but it only matters if the blower can make enough pressure to clear out the lines in the first place. Most blowers are rated in terms of "H2O, or inches of water height, rather than PSI. The conversion rate between the two is about 27.5 "H2O = 1.0 PSI.I did some more reading and it looks like some are modifying a spare pump cover and connecting the Cyclone there. That seems like it might be the easiest method in my scenario because the waterfall pump drains are right next to some plumbing and there's no way I could get anything to thread in there. Even the drain plugs are hard to get back in.
The question is, when I connected my leaf blower (454 CFM) to the drain port on the cartridge filter, why didn't I get any bubbles anywhere? From my reading the Cyclone is only 140 CFM so I should've definitely seen the air go somewhere.
The way you calculate your total water height is the vertical distance between the water level and the lowest point in the plumbing. A few other factors go into this calculation such as number of 90's and length of run, but they usually don't account for that much of the total amount. Let's say your pool is 8 ft. deep and the plumbing for the main drain goes 2 feet deeper than that, your total water height will come out to a little over 10 feet or 120" H2O. While the Cyclone is only rated at 140 CFM, it is also rated at 180" H2O. So as long as your blower is rated for a more "H2O than the water height for your main drain comes out to, then it will be capable of clearing the main drain (given you also have adequate CFM).
Now here's where CFM plays a role. Of course any air compressor can make over 6 PSI ( 165" H2O), but their CFM values are extremely low. Most regular air compressors won't even make over 25 CFM at open flow, no less under pressure. If you have adequate pressure but not enough CFM, it will either take a very long time or it will be impossible for you to clear out the line. You need a mix between adequate pressure as well as high CFM in order to make the job quick and efficient. Usually blowers with very high CFM tend to make very little pressure, and compressors that can make a lot of pressure tend to have very low CFM.
I hope this helps you understand why some things work and others don't when it comes to winterizing your pool!