I don't know what to make of this. Yes, the regular connection that I sectioned was not fully seated and yes there was excess cement pooled up there. But I can't really see why that would weaken the connector.
For that matter, how does anyone control the amount of cement used or where it pools. Isn't this situation a standard consideration that happens all over the place in any given house? Why can't the fittings handle that?
What the heck does a fellow do when such a pipe connection fails in the walls between floors? Or in the first floor ceiling below the second floor in a two story home?
This whole thing is just plain wrong.
I feel your pain; very frustrating I'm sure.
The ABS cement is a solvent, that is supposed to dissolve the surfaces of the fitting and pipe, then fuse them together as the cement cures. Full depth seating ensures positive contact all around the pipe; the cement is not there as a glue to bridge a gap between pipe and fitting. Of course, some bridging may occur, pass a static pressure test, and be OK for a very long time. As I understand it, cement pooling means that the solvent dissolves more of the fitting than it was designed for, and it could weaken that fitting to a point where the combination of mis-alignment pressures during installation, and repeated hot-cold cycles eventually cause the fitting to fail.
Good workmanship includes:
- pipe and fittings are well aligned so there is no torque being applied to the joint
- pipe is well supported so its weight and the weight of its contents don't add torque
- there are sufficient expansion joints between floors in a combined waste/vent pipe to reduce the effect of heating/cooling cycles
- pipe is cut square, interior is deburred, and exterior is slightly chamfered to ensure it can be fully seated into the fitting without scraping all of the liquid cement out of the joint
- pipe is fully seated in the fitting
Skipping any of those steps can reduce the lifespan of a fitting. I'm not a trained plumber; just a homeowner that curses the shoddy ones.
To get at my most recent DWV project I had to cut open the finished drywall in a few locations - suggest you cut your drywall along the centres of nearby studs, and no closer than 6" from the ceiling or top of baseboards to make your drywall repairs a bit easier. Make your hole big enough the first time to do all your work in since it's the almost the same effort to patch a big one or a little one.
There is a chance that your DWV was installed by a professional plumber along with a poorly trained/supervised helper, and you've already found all of the helper's connections that are likely to fail. It wouldn't be wrong IMO to continue just dealing with the problems as they show up. Or, maybe not... Tough call. My experience with insurance claims is that they'll cover the cost of the damage, but not the cost of the repairs. e.g. a wet ceiling/floor/wall will be replaced, but if you cut open the ceiling/wall/floor as part of a repair it won't be covered.
If you do decide to bite the bullet and redo everything for peace of mind, suggest you open everything up before you start re-work and then work from bottom-up without trying to keep up-stream fixtures operational as you go. Working in the middle with 2 fixed ends is slow, hard going and typically adds unwanted stress to fittings. I foolishly did not take that path and had a very frustrating time rolling around in the crawlspace.
G'luck!!!