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The reason the PVC cement didn't work is because it is not meant to be used as a sealer. It is designed to "weld" two mating pieces of PVC… for example a pipe and a coupling of some kind. It does not bridge gaps like an adhesive, but instead partially softens and dissolves the pipe, making for a permanent connection between the two parts. Once set… usually within a minute… the joint is beyond permanent!
You put your finger on one "right way" to do this repair... cut the
joint apart and replace whatever parts you need to. However, there is another
way that plumbers use that can save you some work. Instead of trying to replace
the parts with PVC, you can use neoprene couplers. These are rubber sleeves with
metal clamps that can firmly connect two sections of pipe without the need for
any cementing at all! They can be used not only with plastic pipe but also
copper and cast iron pipes, too. They are meant for drain pipes only! Using them
requires that you cut the existing pipe apart to allow the placement of the
coupler. Once installed, they will give a lifetime of service. One additional
tip… if the pipes tend to sag at the coupler, use some plumber's metal hanging
tape to add additional support for the pipe.
If you want to "stall" doing the big repair for a while, try this:
Get the joint as dry as possible. Use a heat gun to evaporate as much
moisture as you can from the joint. Rough it up with some fine sandpaper and
then wipe it with alcohol to clean off any dirt or oils. First, go buy a tube of
my favorite glue, GOOP. Slather it onto the joint, covering at least 1/4"
on either side of the joint with a thick layer, and pushing it into the joint
seam as much as possible. Try not to run water through the joint for at least 6
hours, preferable 12 or more. According to the GOOP guys, you will have full
strength in 24 hours.
If you do a good prep job, the GOOP will probably stop the leak for months. I can't really consider this a permanent repair, but it is a good stopgap.
Epoxy putty would not be my first choice. Even with good preparation… sanding and cleaning… the repair will probably only last for a short time because the "mechanical" attachment of the epoxy to the surface of the pipe is not extremely strong. Part of the problem is that the epoxy is almost inflexible when fully hardened, while the pipes expand and contract more readily. This varying expansion-contraction inevitably leads to failure of the bond and recurrence of the leak. Think about it… if this was such a great product, why don't the plumbers use it all the time? Because its failure eventually leads to angry customer callbacks… something that no responsible tradesman wants!!
A last word. Whichever temporary repair you try, just keep a pan under the drip to cover your stopgapping-self… just in case!