Expert: Dan Griffin - 3/2/2009

Question
QUESTION: Home Remodel of 30 year old house. I am re-attaching a new PVC vanity drain pipe to the original ABS bathroom drain above that serves a vanity and tub (not a waste drain). In making the transition of materials I used Oakley's Transition glue and followed the instructions exactly. As hard I as I held the joint in place the coupler still left about 1/8" gap. I have tested the drain with water and so far not leaks. Before I close the wall in I wanted to know if it would be advisable to either wrap this slight gap with Teflon tape or fill with silicon caulking? My only concern would be any conflict in introducing another chemical to this joint.
Thanks,
DSR

ANSWER: David, I assume you mean Oatey brand glue.  I also assume you mean the can with the green label that is made for joining ABS to PVC.  If you did follow the manufactureer's methods you did NOT use a primer.  The heavy gel of the green cement is made for making up gaps,etc, so I am surprised that you feel you did not get a good joint.  I suspect you did not put the adhesive on both the pieces of pipe or were very sparing in your application.  When I use any of the Oatey products, it seems that there is a substantial squeeze out of excess glue.  I think I am correct to say that the green cement is not a solvent type cement that actually eats into the pipe.

I cannot think of an easy way to plug up the pipe beleow the new joint so that you could flood the joint to inspect for leaks.  You might completely fill the sink and release it all at once while you watch for any type of leak.  The other thought would be to use the dauber to deliberately fill the visible gap.  A bit of masking tape on the pipes
would keep the joint from looking like a kid did it as you force the adhesive into the gap(s).

Hope any of this makes you feel better about your plumbing efforts.

---------- FOLLOW-UP ----------

QUESTION: You Are Correct that the product is Oatey's' Green Transition Cement and that I definitely did not use primer for this PVC coupler-to-ABS stem connection. I believe I was fairly liberal in my glue application to both parts and some did in fact squeeze out (not enough to "ooze"). I pulled the two together as tightly as I could for at least 30 seconds and when I released it it pulled apart just slightly (perhaps a generous 1/16"). It is this movement after holding 30 seconds that concerned me the most as it made me question the integrity of the joint. I've poured several pitchers of water to simulate a full sink draining as you also suggested and no leaks were visible. My quick online research indicates silicone should be fine but I like your idea of using more of the Oatey's glue. However,my concern is that per the can's directions, #4 states "Apply thin coat of cement to inside of fitting; avoid puddling of  cement. Puddling can cause weakening and premature failure of he pipe or fitting". Would a coat of new cement over the existing cured cement in any way weaken the original joint? I don't have enough remaining ABS pipe in place to cut this joint again so my options are limited.(I have attached a photo)
Thanks again,
David

Answer
David, the picture looks to me to have glue showing on the top of the joint which is where I had concerns.  I was afraid you would have a sewer gas problem at the top, you have tested the bottom and it appears to be holding.  My strong opinion is that you are finished, leave it alone, you're done.  Applying more glue should not create any problems in my opinion - I would go ahead and add the glue just because.  Silicone will make it look like kids' work and prevent any other solutions.  

It is qitie normal for these joints to push apart slightly if you release them too soon.  In the future, push them together and give a 1/4 turn twist as you hold - you will feel the adhesive grab making it hard to impossible to turn to know when you can let go.