I just installed solar heating which pushed my 2" to 1 1/2 in. I oringinally used only the pvc glue and it leaked everywhere, I pulled it apart, used the pvc primer with 3 coats and then the glue. not a leak anywhere. (actually read the directions the 2nd time). The pvc primer, when used correctly, softens the pvc and actually serves to weld the pvc together.