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Does anyone know why water starts leaking from the hole under the sink, or why this hole is even there to begin with?

It seems like as the water builds up in the sink when running through high pressure and volume, water starts to leak a lot from that hole.

enter image description here

enter image description here

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  • when you say incomplete sink drain installation, are you referring to the gold piece connecting to the bottom of the sink drain?
    – Jason
    Jan 17, 2023 at 1:17
  • No, but tell me this, does your sink has a overflow hole somewhere just below top
    – Traveler
    Jan 17, 2023 at 1:20
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    @Ruskes The overflow section seems to be facing/towards us. Think that hole is just an air/vent hole for firing of the sink.
    – crip659
    Jan 17, 2023 at 1:35
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    "It seems like as the water builds up in the sink...", are you saying that it only happens when there is deep water, like with the drain stoppered and you are filling the sink up? Jan 17, 2023 at 2:38
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    It's not the overflow. You can clearly see the overflow construction in the second image. That chunky bit from the drain extending out is the internal plumbing for the overflow drain, and is clearly not decorative and there's no reason to feed the overflow from the front to the rear of the sink.
    – Nelson
    Jan 17, 2023 at 16:35

8 Answers 8

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First of all there should not be any water there and coming out.

The hole is probably a part of sink manufacturing process.

So where does the water comes from.

Probably from leaking faucets.

Your statement that it gets worse with high pressure and flow would support that theory.

Inspect the faucets installation

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    I agree with "Probably ...." I can say with some confidence the leak is where those two black hoses join the spout. Hopefully just poorly connected, or one of them is cracked. Possibly the spout is faulty but hopefully not. There is no path for water from the overflow system to where that hole is.
    – jay613
    Jan 17, 2023 at 14:28
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Try pouring water into the sink instead of from the faucets. That will tell you if its the faucets leaking or the drain. Like Ruskes said, that hole looks like a manufacturing aid. I would call the maker of the sink and ask them. It could be the sink has an internal flaw/crack.

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    An enhancement: 1) fill a bucket from this sink. See if running the taps into the bucket causes the leak. 2) Pour the bucket down this sink. See if that causes the leak. This will tell you with certainty whether the problem is with the supply or drainage of the sink. My bet is on supply. I think the sink bottom between the overflow and the back wall is single-wall. So nowhere for water to flow between them.
    – jay613
    Jan 17, 2023 at 14:19
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    It's not the overflow. You can clearly see the overflow construction in the second image. That chunky bit from the drain extending out is the internal plumbing for the overflow drain, and is clearly not decorative and there's no reason to feed the overflow from the front to the rear of the sink.
    – Nelson
    Jan 17, 2023 at 16:35
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This is how your pop-up drain look like:

enter image description here

It is designed for the sink like that:

enter image description here

The sink has an internal compartment that connects the round hole in the sink bowl to the drain hole that is leaking. It also continuous with the drain hole in the pop-up drain.

Water from the faucet gets inside the pop-up drain internal hole and fills in the internal compartment of the sink, causing the leak.

You need to install a separate drain connector that joins leaking hole to the drain. You are using wrong pop-up drain for the sink design you have.

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    -1 I don't think this is the case. OP's sink has the overflow hole at the front, opposite the faucet, and the hole in question is on the other side (below the faucet). You can also see the rectangular porcelain overflow channel in the top left corner of OP's second photo.
    – TooTea
    Jan 18, 2023 at 7:43
  • @TooTea reviewing the pics, it makes sense. Can there be a crack inside the sink that bridges overflow to the leaking hole? otherwise, i have no idea how it's possible Jan 18, 2023 at 22:00
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    @aaaaasaysreinstateMonica it makes perfect sense if there is a plenum between the basin and the sink bottom. The water would naturally flow to the bottom and out. You have a hole in the opposite side to prevent any pressure effects. But if the bottom is plugged, the plenum is full of water. No idea if that's the actual situation, but it's a coherent explanation.
    – fectin
    Jan 19, 2023 at 5:39
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Drawing of sink

Hello, I believe the issue is with the seal between the waste fitting and the sink itself. With the waste shut, the sink should hold water, but instead it's bypassing the seal and starting to fill the hollow sink before flowing out through the hole left from the casting process. You will need to remove the waste fitting and inspect and likely replace the seal. Please note that this is not the seal for the plug itself, as if it was bypassing the water would go down the drain and you'd only notice the level dropping.

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  • This was my first thought as well. Either the seal between the gold drain and the sink body has failed, or the hole in the sink was chipped/cracked when installing the drain assembly. It seems to work well enough, until the sink fills and the pressure builds.
    – bta
    Jan 19, 2023 at 1:25
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That hole is too perfect to not be man made. OP stated it is a new sink. I believe it is a manufacturing defect. The faucets look to be mounted to the counter, with the sink undermounted. Therefore they would not have any bearing on the water leaking from the hole. Perhaps the drain is not compatible with an overflow and not sealed well. Any water leaking from around the drain backs into the overflow channel and makes it's way out the hole. So this could be a combination of issues resulting in water from the hole. ( just a thought.)

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Something similar happened to one of my bathroom sinks but it does not have that hole. Water would leak from the faucet down the back of the sink. Maybe the water coming out of the hole is actually from behind the sink where the faucet is mounted. Use a mirror and flashlight to check.

The faucet I bought was a name brand from Home Depot and like a lot of these new faucets looks nice but is just painted hollow plastic with a plastic tube that runs to the end of the spout where the aerator screws on. When the water was running high volume it could not overcome the resistance of the aerator and would leak at the aerator connection. It was visibly different, I could see water running outside the sides of the aerator, not just the bottom of it. And when that would happen a tiny bit of water would run down the outside of the tubing inside the hollow area of the spout, and out the back of the sink.

The aerator did not have any debris in its intake screen and that surprised me. It was simply either the aerator was not tightened enough or the washer was bad. Replacing the washer and tightening the aerator (just until water didn't run out of the sides, hand tight don't crank down on it) solved the problem. Good luck.

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Let's start off with some basic diagnostics before calling a plumber (who will do the same thing for an hourly fee).

Testing the sink

You should engage the stopper at the bottom of the sink and then fill the water to just below the overflow hole of the sink (the chrome port in your picture). Dry everything off underneath and let the sink sit for an hour or so. With water just sitting there, you should have no leaks. If you do, it's most likely the drain assembly at or below the bowl.

Testing the faucet

If at all possible, turn on the faucet to where it leaks and crawl in on your back with a flashlight. Can you see where the water is coming from? If so, you've solved the mystery.

If you can't see where the leak is, the next step is to disengage the faucet from the sink. There should be a ring or set of screws to do that. Don't disconnect the water lines yet. Now, lift up the faucet, turn it on to leaking, and lift the center assembly up to look for leaks. You may have to repeat these steps for the handles, since they are a separate piece.

These are your only potential sources of a leak. Be tenacious and you can find the source.

Fixing the leak

If it's the drain, re-seat the assembly and make sure to tighten it up. Use some petroleum jelly if need be to help the seals engage better. The "wedge" screw-in seal at the bottom of the assembly can sometimes be problematic if the sink has slight manufacturing defects in the hole.

If it's the faucet, it could be the supply lines weren't tightened properly. Some of the fancy faucets have "goof proof" push connectors that aren't as easy as the manufacturers would like you to believe (I had a brand new one that took 5 re-seats to ensure it didn't leak). If it doesn't screw down with a gasket, it could still leak.

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    "You should engage the stopper at the bottom of the sink and then fill the water" --> If the leak is from the faucet and not the basin, a slow leak from a running faucet may then show as a basin leak. Maybe fill the basin from another source or do the faucet test first? Jan 17, 2023 at 15:12
  • Another test is to turn the taps on full blast while filling a bucket. The drain part of the sink won't be involved at all, so any leaks you see will necessarily be from the faucet side of the plumbing. If you see a leak, narrow it down further by re-testing the hot and cold sides separately.
    – bta
    Jan 19, 2023 at 1:31
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@Ruskes stated the correct answer in the comment: "incomplete sink drain installation. That one would be for sink overflow. But considering how the rest of work looks like it is not a surprise."

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    In what way is the hole under the sink for overflow protection? The overflow protection hole is shown in the first picture, at the bottom, with a chrome trim ring around it. That hole leads through a channel built into the sink that runs to the drain.
    – FreeMan
    Jan 17, 2023 at 15:54
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    Not in every kind of sink. Some require a separate connection
    – FosCo
    Jan 18, 2023 at 16:14
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    I'll wave the white flag, then, as I've never seen one that requires a separate connection. However, the 2nd pic that the OP provided doesn't seem like there is anything in that design that would make it easy to attach any sort of drain to the hole where the water is obviously leaking out...
    – FreeMan
    Jan 18, 2023 at 16:23
  • That's right, I may be wrong, it was just the most obvious explanation to me.
    – FosCo
    Jan 19, 2023 at 17:49

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