My question is about ABS 3" pipe
l've roughed in my toilet 12" from the finished drywall. l now want to install tiles and therefore need another 5/8". l have yet to secure the toilet flange to the sub floor and therefore can pull the flange 5/8 from the wall which in turn is bending the 3" pipe and connections running from the flange to the main stack about 4' away. So my question is will this stress on the glued ABS joints over time loosen and start to leak?
I've had ABS drain pipes in my home since it was built in 1977.
In my opinion and experience, the answer to your question may be "yes".
If it were me, I would simply cut the pipe and add another coupling or two to relieve the joint stress, using ABS glue only of course.