recurring leaks in under-sink drain plumbing

[thaddeus cox]

Hey all - I know this probably isn't the ideal place to ask this question, but I'm sure you-all will have answers/opinions. :)

I had my kitchen remodeled a few years back with all new supply and waste plumbing to the sink/disposal/dishwasher. The waste plumbing is threaded black ABS pipe.

Twice now over the course of 2-3 years, I've gone under the sink to discover a puddle from where one of the fittings has loosened (I assume from temperature differentials?) and started to leak.

The first time I figured it was a fluke. This time it was the collar where the main sink drain goes into the waste pipe. In the course of my fiddling around trying to figure out what was leaking, that fitting came entirely apart.

I figured out how to get it back together and hand-tightened it and all the other fittings. So far so good as far as leaks.

So... I guess my questions are as follows:


Does this sound like a common occurrence with this type of installation? It seems like the common homeowner might suffer significant damage before discovering something like this.
Do you think this a case of "the plumber forgot to tighten the fittings"?
I assume there's no cement or other compound required on the threaded fittings?
Is hand-tight appropriate? I was concerned about over-tightening and damaging something.
Is threaded ABS common/standard these days, or do you think this is an inappropriate application since it sees a lot of thermal extremes?
Do you think this is a result of the plumber doing "something else" wrong that I haven't considered?


Thanks in advance for your input.

[Garry Sorrells]

Your disposal is probably creating a vibration that is loosing the connections. Hand tight is the norm though it differs depending how strong the tightener is. Try running the disposal more often with less in each batch or slower feed of materials into a running disposal.

Put yourself on a maintenance schedule to tighten the fittings.

[Ian Page]

Threaded ABS is commonly used in this application and IMO preferable to 'slip' or glued joints. ABS typically has a longer life than brass or copper pipe and significantly less expensive. Threaded joints make for easier repair or clean-out. Glued joints, especially those in close proximity to the disposer have a tendency to break from repeated vibrations especially if the wrong (non-ABS specific) glue was used. My suggestion is, hand tighten all the threaded joints, run hot water through the waste and hand tighten again. Thermal expansion/contraction should not be a significant issue but over time threaded joints can/will loosen. Though generally not a good idea to mix and match metal and ABS fittings, IMO the upper-most threaded nut which attaches the tail piece to the sink strainer should be metal (usually a brass alloy) which requires more than just hand-tightening to effect a tight seal. If it came apart it's either defective or not installed correctly - perhaps cross-threaded.

Another possibility of water leakage is that the required / necessary slip seals between the fittings are missing or even in place but split. Typically threads should not be glued but it certainly doesn't hurt to coat them with pipe compound before connection. As Garry said, regular maintenance prevents a bunch of bad stuff happening.

[John Kogel]

The trap is meant to be removable, unless it has a large drain cap, large enough that you could remove a ring or an earing.

It should stay tight now that you have retightened it. If it doesn't, it is cheap and easy to replace.

[thaddeus cox]

Thanks for the replies guys.

I'll keep a closer eye on it, and I'm also considering getting a few cheap water alarms.