This is done by heat & pressure using no glue.
In this picture a 4' length of pipe is in the machine where it will be
welded on to a tee fitting and used as a cleanout

The ends of the pipe and 1 end of the tee are cut even.

Once squared, a heating pad heats the ends of the pipe to 475 degrees.

Once the ends are hot enough, the heating pad is removed and the 2
ends are pushed together. A large bead forms on the outside and inside
of the welded joint. This is from the pressure as the ends are pushed together.

HDPE Fusion Welding Process | Pipe Bursting Method 1 | Pipe Bursting Method 2 | Trenchless Water Line Replacement