Winterizing Pool Water Line

[joemost]

Hi Everyone,
Unfortunately before a member of my family was done winterizing the pool, he passed away. Leaving it on me to finish winterizing the pool. He had completed 90% of winterizing, with the exception of the water slide line.
The water slide line is connected to the water return lines, with a valve that redirects the water when we decide to turn on the water slide. The water slide line is the black flex pipe to the right in this photo: https://imgur.com/cgsqNYY , the regular return lines are the two pipes going into the ground.

My attempt to blow out the lines was to use this 'spa blower' he haad which basically was a leave blower. The return lines pipe was disconnected from the filter (each pipe is about 2 inches with threading, and then a union ring is used to connect them). I didn't have a fitting so I tried to create a seal with duct tape, didn't really work as when I turned it on I could feel air coming back.
Basically my process was just running the blower with the water slide valve opened up, I don't think the pipe was pressuring as I could feel a lot of air escaping through my makeshift duct tape seal. I think from my physics 2 days air is just going to escape from the area of the least pressure, so I won't be able to push out the water unless the pipe is completely sealed off.

Heres basically what my makeshift operation looked like: https://imgur.com/Bv1MHIb

The water return on the slide is about 7 feet of the ground.. so I think it would take a good amount of pressure to push all the water out.
The pipe has a thread like this : https://imgur.com/ImcoBtN on it. My guess is I need to get a better seal and then use my air compressor, so I am wondering if there is some sort of compressor fitting I could thread into this pipe with that union piece. Does that make sense? Is my process flawed, I figured all I need to do is create a clean seal and push air in to eventually push out any remaining water.
I put a bunch of reference pictures in this imgur album: https://imgur.com/a/frgGx Any help would be huge.. don't want frozen pipes.. I've had it in the past and shoveling stinks!
Thanks!
so in summary my question is: Is my process flawed, I figured all I need to do is create a clean seal and push air in to eventually push out any remaining water. So basically I need to find a compressor fitting for the pipe (which I think is 2 inch).

[Denniswiseman]

Is the pipe from the pad to the slide buried. can you disconnect from the slide and the pad and let most of the water drain out and then blow the rest
Also the rubber hose would stand freezing

[Teapot]

Seconded, that pipe could be disconnected at the jubilee clip end and just drained?