Just one last note, JET.
At the risk of stating what might be the obvious (and as I noted in my first post above), the chemical reaction of the glue during the bonding process causes rejection. The pipes actually push apart and separate during the cure. This occurs only during the seconds after they are initially pushed together. It is critical to maintain pressure on the connection (continually pushing them together) for the time it takes for the chemical bond (melting and curing of the plastics at the joint) to occur. This is usually no more than 30 seconds or so maximum; maybe less...but unsure on 12" pipe. That is why I always use a sharpie marker to measure back from the end of the male pipe and mark on the pipe exactly how far the female side will ride up over it. That way I can watch and verify that A) the pipe connection is seated all the way in B) it is not being rejected or pushed out.
