My 2 bowl kitchen sink has PVC drain pipes. The elbow that connects the two bowls just came loose from the tail piece. All of the pipes were replaced this summer. Why would it come disconnected? And is there anything I can do to prevent this from happening again? :confused:

Well... I am going to assume that the plumber used a jointed system... that is, that every joint or so there is a nut in place.. yes.. Then must end into something solid... like a copper p-trap or a pvc p-trap... or maybe just a fitting sticking out of the wall.

Either way... you have an issue. My opinion, pipe it solid pvc... then only two nutted joints will be at the transition from the pvc to the tailpieces of the strainer assemblies.

But for now, just loosen nut a bit... reposition piece... and then re-tighten nut. Then, for now support that pipe with a bottle... a brick... you know.. something that will fit underneath and hold it up. If you intend to keep this system as piped then you will need to install a hanger of some kind under this joint.

These systems are famous for slipping (over time) if not hung/supported properly. If you have solid pvc then may have to lengthen pipe up to sink tailpiece to take pressure off the desanco type fitting.

Anyway... see if this info. Helps... get back to us.

If answer helped please RATE THE ANSWER below. Thank you.

All of the connections are slip joint connections from the tail pieces, to the 'T' fitting and through the 'S' trap ending at a threaded connection on the solid PVC pipe going through the floor. I re-tightened the offending joint, and it feels very solid. I attempted to re-tighten all of the other nuts, and none of them would turn more than a 1/16 of a revolution, or so. I can't believe that my drain piping is unique, and if this was a wide spread problem, I would think the lawyers would be all over it (I'm in the U.S.).
Is there a specialized hanger for this situation? There is nowhere to attach to the bottom of the sink, so the only thing I can envision is a strap that runs from something solid behind the sink to the underside of the counter.

You don't have to "hang pipe" to support it. You can support from the bottom or the back easily. The pipe support consists of a threaded plate + 2 screws + locknut + all thread + locknut + pipe support. All items are bought separately. Look here:
Pipe Hangers

The two major components are the ceiling flange and the split ring.

Thanks for the back up KISS. Bigron... as KISS said. Good luck!

I suspect that the tail pipe is not extending down far enough into the elbow or turn of the arm to the trap. Either that or the nylon seal under the nut is missing or defective. If the seal is too close to the end of the pipe, there is enough flex in the pipe so that you do not get the necessary mechanical bond needed. You didn't say but I get the impression that this happens on one side only. What's different from the other side?