Home Depot time
I would tie in my drain line on the pipe in the front of the photo - closest to you.... the white do-hickey on top is a "pipeless vent". Find adapters
(Home Depot should have them - and I'm pushing them because I just bought a few thousand shares ..
) - to:
1. screw into the fitting coming out the side of the pipe. - though you may end up cutting into the pipe below the present screw fitting because I've not seen a screw in adapter that would do what you intend. Still an easy fix.
2. Reduce to a garden hose fitting.
Total cost - less than 10 bucks...
3. Elevate your dehumidifier so the drain pipe is above all connections............ hook up and go........
Remember the most important part of this thread.......... I'm not a plumber... just a DIYer who improvises frequently - but tries to do things reasonably proper.......
If "Jimbo" (or anyone else for that matter) overrides me......... take his advice over mine......