What is he doing wrong?

[thomashansen871]

https://youtu.be/tj2mJBMT1zQ

[DrTimPerkins]

First, I'd note that he is doing several things correctly, and looking at the other videos, the system overall looks well installed and maintained. Given that, I'd say that there are a couple of things that could be done differently.
1. Don't put spouts, tubing, or fittings in your mouth or wet them with spit. This introduces microbes into the system.
2. Some of the terminology used isn't correct (lateral line, dropline, mainline).
See https://www.youtube.com/watch?v=c6lpMgsfF-c&list=PLZP4fDl-nB9-4aZkQyDR070QpxcAr02q5&index=9&t=33s for proper terminology.
3. Not a big deal, but there is no need to be worried about crud on the outside of the tubing. It is aesthetic only.