I used Glued ABS (?white plastic stuff sold for water pipe) for air lines at 125 psi in my old shop. I used the same pipes for 15 years and never had a problem with them. Would do it again in a heartbeat.
I also soldered a large number of joints in a refrigeration system using copper pipe (many more joints than the average system, because of the home-made kludged up nature of the beast I was working on) with
50-50 solder. Worked perfectly, never leaked.
I also used Sil-fos, and I liked it better. Not so touchy about getting the solder flowed in the whole fitting as soft solder. Soft solders with a little antimony are stronger,(Pb95-SB5) and solder just as easily. Avoid HMP 95%lead,1.5%silver,SN the rest). Melts at high temperature and is weak mechanically.
The REAL magic trick in soldering copper is to clean the pipe until you see shiny copper before you solder...but I would still use plastic....