Yes, the flexible accordian-style sink drains / waste pipe are sold at the local hardware stores. That doesn’t mean that they are a good idea to install under your bathroom sink.
Why are accordian drain lines bad?
The quick answer is that they have a tendency to clog at a much greater rate than smooth-walled pipe. Plumbing standards today require a smooth-walled pipe capable of self-cleaning to be used for sink drains and waste pipes. What is self-cleaning? The swirling action of the water going down the pipe creates enough friction to “clean” the inteiror of the waste pipe, at least in theory.
When you install a corrugated flexible drain line in place place of a more rigid tailpipe, you now break up that swirling motion and the pipe will no longer clean itself. Furthermore, the indents of the pipe are significantly more likely to catch debris, grime and other nastiness, further reducing the flow of the waste water. Think of things like hair and makeup that has been washed down the drain collecting in those grooves.
The third reason most flexible drain lines are bad is that, to me, a home inspector, it is indicative of poor workmanship or at the bare minimum, someone who lacked the skill needed to line up a two reasonably flexible and thin-walled plastic pipes to drain appropirately. I’ve never been to plumbing school, but I imagine by the second day they teach you how to hookup undersink drains correctly because good plumbers don’t need to use flexible drain pipes in a vast majority of circumstances. There are situations where the flexible drains are basically the only thing that will fit in place, but these are exceptions.
Usually when I see a flexible accordian drain pipe, it is a dead giveaway that a home-owner or a house-flipper did the work, rather than a competent plumber. Not that a home-owner can’t replace a drain pipe, but that they are much more likely to leak when the home-owner does it.
There is one type of flexible waste pipe that is “less bad”.
A few times I’ve run into a grey flexible drain kit that always has a sticker on that says “meets UPC #xyz” or something to that effect. I’ve seen it sold under the name of “universal drain kit” and it is considerably more expensive than the regular smooth-wall pipe you should be using. When this particular kit has been installed, the drain usually doesn’t leak. I also do know that these kits aren’t corrugated; they have a smooth interior wall that allows for better waste water flow. For this reason, I won’t write them up on a pre-owned or older home if the install looks like it was performed in a workman-like manner and isn’t leaking. But on a newly constructed home, it better be the right pipe. No exceptions!
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