My new house has had some vent/sewage leaking problem. Since I do not see a purple band around the PVC joints, I suspect that primer was not used. How can one know that for sure? I have a section of a joint cut off (due to a repair), should I look for something purple there?
If you have leaks then it is almost immaterial whether primer was used or not. But unless they were very neat, and neater than they should be since inspectors that require primer like to see the purple band around the fitting, then you should see the primer inside the fitting at the bottom of the joint. Some cements advertise that they are “strong” enough to prime the pipe and glue it in one operation. Some plumbers believe them and it usually does work for several years, but eventually joints start separating. In your case, if the joints were not primed, but you did not have any leaks then, since the pipes are not under the constant pressure that water lines are subjected to, then your system would probably not have had problems. This is apparently not the case, and the best solution may be to redo the entire system, since cutting pieces out usually requires couplings and thus additional joints which can be future sources of problems.