With the tubing expanded, I have a few seconds to push it onto the elbow fitting in the wall. I couldn't see if I was hitting the prongs of the fitting to be sure I had it on all the way, but it was stopping, so I think it was good.
I stuck my phone in the wall and took a picture so I could hopefully see if the tubing was on the elbow fitting all the way. Looks like it was. The white ring is touching those prongs. I'm sure with more experience, I would just know by feel that it was fine.
So I did the same thing with the hot water side, and I'm holding the fitting in place for a moment while the pex tubing contracts and clamps down tight on the fitting.
And this was the upstairs sink all done. From the time stamps on the photos, this took me 25 minutes, but a lot of that was going down to the basement to get tools I had forgotten, and I wasn't rushing at all.
