I'm replacing my water filtration system. The old one used a dedicated drinking faucet. The new one connects directly to the main faucet. In removing the old drinking faucet, I found 3 lines: input, output and a third line that ran to a hole that was drilled into the drain pipe. This was held tight by a bracket that was clamped around the drain pipe.

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My question is WHY and is there some reason I can't replace that section of PVC with one that's intact? Is there something that needs to drain there that I don't know about?

  • Has there always been a hole, and didn't it leak?
    – Huesmann
    Commented Feb 8 at 13:19

2 Answers 2


I'm sure that if you searched the internet for instructions <brand> <model> for the old water filter system, you'd find that it has, for whatever reason, a drain line. This drain line was tapped into the PVC tail pipe so it wouldn't flood your sink cabinet.

If your new water filter system also has a drain line, then you've already got a handy place to attach it, so no, you shouldn't replace this tail piece. If the new drain line is much smaller than the existing hole, you'll probably need to replace it and make a hole suitable for the drain of the new filter.

If your new filter system does not have a drain line, then it's pretty much guaranteed that if you run water down this drain now, you'll get water under your cabinet, so it is highly recommended that you replace this piece of pipe with a hole in it with a new one without a hole in it.


Yes, just replace the pipe. Note it's not just a piece of PVC pipe, it's a sink tailpiece that has a flange at one end. Remove it and take it to the store to make sure you get the right diameter and long enough. May as well buy one with a dishwasher connector on the side, that you cap, so that in future if you need to connect a filtration system (or a dishwasher) to the drain, instead of drilling a hole you use an adapter to the dishwasher connector.

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