Sink Water not Draining, No Blockage

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Peter Dolan

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Hello everyone,

I was wondering if anyone could help me with a problem I'm having with a sink I'm fitting not draining even though there isn't a blockage (maybe).

Quick background, I am putting the sink into my wife's business. There was a large ceramic sink with copper and steel piping that has been there for about thirty years that eventually fell off the wall. I am trying to replace it on the cheap as it is only used to fill up buckets of water etc. and doesn't have to look amazing or anything.

Anyway I struggled to find a u-bend in the local hardware store that fits up to the 1.5" sink end and 32mm pipe end. In the end I have concocted one myself using some 32mm pipe, a couple of 1.5" to 32mm gaskets and some of the pieces of a u-bend I purchased.

However for the life of me I cannot get the water to flow... I have checked the pipe from the wall, inserting a two metre snake and pouring water directly down there, it isn't blocked, so the problem definitely lies with the drainage system I've installed to the sink itself.

In order to get the 1.5" end of the u-bend (unthreaded) to connect to the 1.5" end of the pipeline in the wall (just a metal end of a pipe, no thread) I cut a small piece of 32mm pipe and used two 1.5" to 32mm gaskets to join it together.

However this is very hard to connect up... I can put the gasket into the end of the metal pipe in the wall no problem, but not with the 32mm pipe already inside it, it's impossible to push in. I can, with a lot of effort, push the 32mm through the gasket once it is in the end of the metal pipe. Then I need to push on the end of the u-bend with the other gasket on the end onto the protruding piece of 32mm pipe, but I think as I do this it pushes the 32mm section through the gasket on the wall even further and that in turn blocks the flow of the pipe in the wall (hopefully my crude diagram will explain). If that's the case any idea how I can get this rigged up without pushing the pipe all the way through? Or is something more obvious causing the flow problem?

Any help would be greatly appreciated!

Pete.
 

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Terry

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You may have too much piping going into the wall.
I sometimes follow other plumbers and find that the p-traps were not trimmed shorter before installation.
I like to have them cut to length where it would meet the wall if possible. That way nothing is blocking the fitting that is in the wall.

By the way, nice drawing.
 

Peter Dolan

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Thanks for the compliment, the drawing went a lot better than the sink installation so far...

It might however be a little misleading, I drew the 32mm pipe a bit exaggerated to show where it goes, it is in actuality only the length of the two gaskets fact-to-face. However it still pushes through when I try to push it on to connect at the wall it seems. So it will only end up a little in the frst gasket say and then out the back of the second one and ultimately blocking the flow down the exit pipe. At least I think that is what is happening...
 

Peter Dolan

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So I have been back to the drawing board and tried again with the sink and now I know exactly what is happening with the water flow... but I cannot for the life of me understand it. So far as I can tell it is witchcraft or a glitch in the matrix or something. However I am hoping it will turn out to be some basic plumbing physics I wasn't aware of.

Anyway it turned out the 32mm pipe was not blocking the mouth of the final exit pipe. I put a camera through the drainage from the sink and could see that the water simply stops, without any reason I can understand, after the first sharp bend in the pipe... I could see from the light from the camera inside the plastic pipe where the water level was and on the relayed picture from the camera itself that in the second section of pipe there was no water... I know there is no blockage as I have taken these pipes off plenty of times over the last few days, they are newly bought, I can see right through them and the camera itself was running through the pipe as well anyway... No matter how much I run the water it just fills up in the sink but doesn't flow round the corner of the pipe. If I leave it for ages the water does eventually dribble over the bottom end of the exit pipe ad make it down the exit pipe, but it is so slow you almost can't see the water level slowly dropping in the sink.

I have attached another diagram that hopefully shows what I mean better than I can explain it.

Anyone have any idea why this is happening?!
Sink2.jpg
 

Peter Dolan

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Well I guess it is supposed to visually show what I was trying to explain. That the water sits in the sink above the drainage pipes and won't flow around the corner despite there being no blockage... and I've no idea why...
 

Reach4

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Well I guess it is supposed to visually show what I was trying to explain. That the water sits in the sink above the drainage pipes and won't flow around the corner despite there being no blockage... and I've no idea why...
You are right. It does picture that, and I wasn't thinking right.

That water rising to F would seem only be explained if something was blocking even air from passing through L.

As a quick test, try pushing a soda straw through the drain to about spot C or D (in the marked-up picture). See if that causes flow. Does the water level really rise as high as F? How high can you get that water to rise (without coming close to overflowing). What this is about is that an overflow path on a sink not only can run water below the stopper, it can also allow air trapped in the tailpiece to get out. Many new bathroom sinks (especially some "vessel sinks") don't have an overflow, and lack this air escape path. You have an overflow. Maybe it is blocked? The straw test may not help, but it is easy if you have a straw.

I suspect there is actually a vent at place M. Your pipe after the trap should have a vent. However lack of a vent does not normal prevent draining.


img_2.jpg
 
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Peter Dolan

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Hello,

Thanks for the advice guys. I am not sure what the overflow refers to exactly... if you mean the sink overflow then there is indeed one, but the water is stopping at the bend in the pipe way after that (I have added the sink overflow to the little diagram below and you can see it in the picture of the sink I attached in my first post) so I don't see how that would vent anything off, that is just filling up with water as well to the same level as the sink.

I ran some tubing down the sink (green line on the diagram below) and the water began to flow. After a while water then started to come out the sink end of the tubing, the physics of it all is starting to blow my mind. Anyway, I guess that proves that there is some sort of air pressure in the pipe that is causing the water to not flow out of the sink right? There is absolutely no blockage in the pipeline whatsoever.

In answer to your other question I have filled the entire sink right up, even past the overflow (marked number 1 on drawing) and nothing starts to flow down it as it is at the moment. It will drain eventually but only at an incredibly slow rate. I also had a feel around for a vent at the top end of the pipe at the wall (point M on Reach4's diagram) and there was nothing there...

What should I try now do you reckon? Am I able to put a vent of my own into the pipe where the red circle is on the diagram do you think? What would be the best way to do that?

Sink3.jpg
 

Reach4

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I ran some tubing down the sink (green line on the diagram below) and the water began to flow. After a while water then started to come out the sink end of the tubing,
That is mind blowing. Are you saying that the tubing opening was higher than the water level in the basin, and water flowed up and out out of the open end?

You can measure the air pressure at the far end of the tube. The procedure would be to run some clear tubing through a shower trap into the trap arm. Blow to remove any water in the tube.

Take the near end, and put it into a glass of water. This glass could be elevated, maybe somehow taped into the soap dish. Tape the tubing to support that weight to keep the end of the tubing in place. If vented, the level of the water in the tubing should be about the same as the other water in the glass. If there is vacuum in the drain air, the water level in the tubing would drop. This is called an open air manometer.
 
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Peter Dolan

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It did indeed. I am pretty certain this is some sort of siphoning effect that I was supposed to learn in school but didn't... nevertheless that is what happened. And when I removed the tubing the water flow stopped pretty quickly again.

Okay, I understand what you mean, that can be the next thing I will try. This sink is taking over my life...
 
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Bannerman

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Without a proper vent in the drain line for that sink, the pressure of the water in the basin was pushing against trapped air, with the trapped air acting as a dam. Inserting the tubing into the basin of water will first allow water into the tube, which was then sprayed back at you when the end of the tube entered into the slightly compressed air-pocket just past where the wall of water was located. Allowing the trapped air to release through the tube permitted the water to flow into the drain line.

An AAV (air admittance valve) installed below the sink will allow air into the drain line to prevent water in the fixture's 'P' trap from being syphoned out from the trap, but because it is a one-way valve, it will not allow trapped air to release.

The correct remedy will be to install a vent line within the wall, which will either tie into another vent line above, or the new vent will need to terminate above the roofline.
 
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Peter Dolan

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Hmmm, I can't really start installing stuff into the wall even if I wanted to. The sink is in my wife's business and it was just supposed to be a quick job...

It's very odd as there was a sink there before which also had no vent and that worked fine...

I guess I don't need to test anything more about the air pressure, sticking the tubing down there was proof enough.

If I was to insert my own vent where that red circle is would the vent line need to go higher than the top of the sink do you think? Or would just up to plug level be enough?
 

Bannerman

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It's very odd as there was a sink there before which also had no vent and that worked fine.
Was the old P-trap a different style than the current one? I have not seen that style P-trap previously but perhaps it is common in Germany.

Your drawing seems to show a vertical barrier at the top of the trap where the flow direction changes. Your drawing appears to be accurate when comparing the actual photo provided. Perhaps the old trap may not have had that barrier which maybe the difference of why the basin will not now drain. I suspect the prior basin was equipped with a different style trap which drained slowly and produced air bubbles that rose up through the water from the drain.

insert my own vent where that red circle is
An open vent at the red-circle, would allow the trapped air to be released, but as that trapped air is actually sewer gas, it would then allow sewer gas to enter the building. A vent would normally be terminated to the exterior to vent the sewer gases outside, above the roof.

As mentioned previously, there are AAV devices that depending on your location's plumbing code, could be installed where the red-circle is shown. As an AAV acts as a one-way valve to allow air into the drain line and prevent sewer gases from exiting into the room, I anticipate an AAV would not be helpful for your issue.
 
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Peter Dolan

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This is the old drainage system. Not sure what kind it is, but for sure there was no vent or anything on it... (the 32mm pipe running out to the right there was longer and ran straight into the wall).

20200613_153710.jpg


The type I am currently using is probably not something you recognise as I had to bodge it together myself out of various pieces we had. It was part of a setup like the little diagram below, with the red bits the bits I took for this project.

Sink4.jpg

I see what you mean about venting the gas into the room, but at the moment the pipe is just sitting there open at the wall, and has been for around a year, so isn't that just the same?
 

Reach4

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Bottle trap, I think. Maybe it could have some drum trap properties (drum trap works without siphoning despite no vent).

I think I might try sticking a drain bladder into something, either down the drain below the overflow junction, or into the wall. Clearly I suspect some blockage, despite tests that take water when the hole is open at the wall.

See if some pressure gets things flowing.

If your drain and wall are perfectly aligned, I wonder if there is something like the Sudor Trap-Vent available. https://www.ipscorp.com/pdf/studor/STU021_TrapVent_web.pdf

However here is the deal: an AAV will not help draining. An AAV only prevents trap siphoning. It is rare to non-existant for a vent problem to be the sole cause of bad draining.
 
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Bannerman

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The old trap appears to have a smooth transition into the trap arm, which likely permitted some of the trapped gas to be pushed out into the basin which then allowed water to flow slowly into the drain. I anticipate relieving some of the trapped gas will have caused gas bubbles to bubble-back from the drain into the water in the basin.

Your latest trap drawing in post #16, shows a pointed section which is above the trap arm. I suspect that raised section will trap a large bubble of gas which will prevent the water to pass by below the bubble. This will be similar as shown in your previous drawing within post #9 above.

Is there an alternate P-trap style available that will fit the available space so as to provide a smoother transition to eliminate areas where a bubble of gas will become trapped?
 
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Reach4

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I suspect the old trap as it has a smooth transition into the trap arm, which permitted some of the trapped gas to be pushed out into the basin which allowed water to flow slowly into the drain. I anticipate relieving some of the trapped gas will have caused gas bubbles to bubble-up through the water in the basin.
Peter has filled the bowl to a depth significantly deeper to bottom of the basin than the trap seal.

The only way I could see trapped air stopping flow is if there is some really big belly in the drain line farther on after the wall entrance. The more I think about it, this matches the symptoms.
img_1a.png


As a workaround, maybe modify that old trap to remove the internal barrier. Or just put a pipe with no trap and let the hidden belly be the trap.
 
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