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B

bf1

Hi everyone,

I have an issue with my bathroom sink. It's been "blocking" regularly, maybe once a month, for at least 3 years. The sink fills with water and doesn't drain. In the past I've used "HG Liquid Drain Unblocker" and that often will clear the blockage, but it doesn't always. I've also called a man out a couple of times to unblock it as I figured it must be blocked somewhere down the pipe, and he's managed to clear it, except the last time when it ran clear for a week and then blocked again. It's been completely blocked now since Christmas 2019.

I say "blocked" because I don't think it's the pipework where the blockage is, and the trap beneath the sink isn't clogged. I'm not even convinced there is a blockage.

Here's some photo's to refer to:
Plumbing - https://photos.app.goo.gl/LgNLshYPqsv5wB6t8

The photo's aren't labelled but if you start with how the assembled version looks here, you should be able to see which bits I've progressively removed.

The setup can be described as follows:
  • sink, which stays filled to the brim with water when the plug is taken out
  • trap (it has a small valve which I think is for negative siphon pressure?)
  • waste pipe going off horizontally to the right (almost horizontal, there is a slight decline so that the water flows downhill)
  • 90 degree bend down
  • vertical pipe going down
  • 45 degree pipe
  • almost horizontal pipe heading off in the direction of the vertical stack that the toilet connects into (I don't know if it actually joins but I am assuming so)

BUT here's the magic:
if I fill the sink to the brim with the plug in, and remove the plug, the water level goes down a small amount (I would say the same amount as would fill the trap). If I ladle all the water out, then put the bowl and towels down to catch the water when I remove the trap, the only water that comes out is from inside the trap. The entire pipe is empty. If there was a blockage in the difficult-to-reach bit where the waste pipe meets the stack, I would expect the pipe to be backed up all the way to the sink with water, but it's not. In 2 of the photo's you can even see when I've removed the first horizontal and vertical and 45 degree sections of the pipe, and no water came out at all (I was expecting the whole thing to be full of water).

I explained this to the man last time he came, that although the sink was full of water, the pipe itself will be empty, but he looked at me like I was a madman. He used tools to push a brush on a wire down through the pipe, and it was connected to his powerdrill to make it rotate. The first time he came, he spent the first hour doing the unblock and the second hour trying to get his drill out of the pipe, he said there must be some very tight bends somewhere. The second time he came, he said it seemed very hard where the blockage was deep in the pipe, that it must be dried toothpaste or something. The toilet in the same bathroom flushes just fine, it's not blocked.

In 2019 I replaced the trap with an identical one, except the new one had the small valve at the top as I thought this might help. When the sink is full of water, if I gently push the pin up, water drips out, which shows that water can get through the trap and out to the waste pipe.

Today I took it all apart again. When I took the trap to another sink and ran water through it out of the tap, simulating a draining sink, the trap filled and the water flowed out of the waste hole. So I know the trap isn't blocked. The pipework was all empty, no water. I put everything back together again, filled the sink with water with the plug in, removed the plug and...the water didn't drain at all. When I ladled all the water out of the sink and took everything apart again, the pipework was, as always, completely empty of water, it was just the trap that was full.

I've also explained it all to my regular plumber, he's really good and I always recommend him to people, but his suggestion was just to use "the most brutal drain unblocker liquid you can buy from a plumber's merchants". But, the pipework is always empty of water, so I don't really understand this advice. But, I also don't know what's causing it all. I'm sure that if he thought there was an issue with the trap and something like trapped air, he would have just said to replace the trap or would have quoted me for fixing all the pipework up to make sure there was always flow. I trust his judgement, and for him to suggest using a drain unblocking liquid whilst he was stood there looking at the pipework as I describe what was happening, he must have been thinking there's a blockage down the pipe somewhere that just needed clearing.

If the waste pipe was full of water, then it seems pretty obvious that there's probably a blockage down there somewhere, but it's not. So I don't understand why the sink doesn't drain if the trap is clear and the pipe is clear. Or, at least seems to be in my understanding.

If anyone can suggest what is happening here, and what I can do to fix it, this would be greatly appreciated.
 
rpm

rpm

Esteemed
Plumber
Have you tried blocking the overflow and using an old fashioned cup plunger?
 
P

PETE 123

Dip in pipework or blockage downstream somewhere trapping water. Water from basin cannot move this water so it stops maybe.
 
snowhead

snowhead

Esteemed
Plumber
It's blocked at or close to the stack, they'll be 1 or 2 90 degree elbows close together and it'll be blocked between them or between the last elbow and the stack.
If you pour water down the pipe slowly and not through the trap or sink the water will go till the pipe fills.

If I was looking at that, first I'd use a wetvac on the open pipe end in the floor to try and suck the blockage back or loosen it.
If that failed I'd try a small flexible rod without a brush on to see If I could get through the blockage before trying anything bigger, something like this.

Drain unblocker.PNG

If all that failed I'd want to see the pipe at the stack and probably repipe it, avoiding elbows and only using bends.

Using acid won't free the blockage, the acid isn't getting into it to break it down.
 
Aquarius

Aquarius

Plumber
Gas Engineer
Have you looked on the actual plug hole waste part? Can’t tell you the amount of times I’ve found all kinds stuffed down there, pencils, straws, cotton ear buds to name a few. Try removing the trap, and run the tap into a bucket to see if water comes out at a decent flow. Failing that, then I’d be looking at the stack as suggested.
 
OP
B

bf1

Thanks for your comments so far.

If I remove the trap and put a bucket underneath, if I look down the plug hole I get a completely unobstructed view of the bucket. The plug hole is basically a hole directly into the trap, so I know it's all fully clear.

If the pipe was fully blocked at the stack end, this would cause the pipe to be empty but the sink full, because there would be nowhere for the air in the pipe to escape to because there's a blockage at one end and a sink of water sealing it at the other end? This would be why the sink doesn't drain into the pipe?

Thanks.
 
snowhead

snowhead

Esteemed
Plumber
If the pipe was fully blocked at the stack end, this would cause the pipe to be empty but the sink full, because there would be nowhere for the air in the pipe to escape to because there's a blockage at one end and a sink of water sealing it at the other end? This would be why the sink doesn't drain into the pipe?
Yes that's the problem.
 
king of pipes

king of pipes

Esteemed
Plumber
Gas Engineer
I would tend to agree with snowhead the blockage is likely to be as the pipe enters the stack , how long is the run 3m is the maximum before a increase in diameter is needed and it must have a continuous fall . Kop
 

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