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I drew a quick diagram here (you will have to forgive the crudeness):
enter image description here

What started as a small blockage with slow draining has grown to be a near complete blockage. We put some water down and over several hours it will eventually go down providing we leave it.

As you can see we have a small circular join that has both the washing machine and sink attached and then a final pipe that leads to outside. The distance between the washing machine and circular join is approx 3 meters of pipe. The washing machine drains fine directly to the outside.

The pipe from the sink however is not. I put a long electrical fish and was able to get to I believe the circular join, the total length was approx 5.5m. The fish passed with relative ease.

I then poured approx 2 litres of salfumant (hydrochloric acid) down the sink pipe and the blockage remained, I could not pour anymore as the pipe was near overflowing, according to some calculators with a width of approx 3.5cm this would mean the blockage is around the 2-3m mark. We left this a couple of days.

Today I bought a draining rod/spring rod like the one pictured, but thicker.
enter image description here

I managed to get this down and after rodding for a while, water and acid began to flow back. I collected this in a bucket. All the while there was a lot of gurgling going on. I am slightly perplexed as to how this could flow back and can only presume there is air pressure or something of the sort in the pipe. Clearly the vast majority of the acid we poured down a couple of days ago had come back.

Im going to try some hot water in a minute and see if it goes down. But does anyone have any experience with this and how would it flow back and up? Built up pressure?

I feel I need to mention, the pipe has a slight decline leading down to the join and has been functioning for approx 5 years with only minor issues. Also the pipe is embedded in concrete as it's the Spanish way. Solid concrete floor which makes it difficult to access any other part of the pipe.

I suppose my question is how did it flow back after being rodded and if anyone has any other suggestion.

  • It does seem like an air-pressure issue, as If there is blockage in the vent-stack. BTW, is that muriatic acid (HCl) going into the washing machine??? It can't be good for it. Also, to remove fat blockage, alkali may work, but not acid (though neither are recommended!). – DrMoishe Pippik Aug 19 at 17:42
  • @DrMoishePippik I can't see anything going towards the washing machine. The washing machine seems to drain well, as though the issue lies between the joining box and the pipe to the sink. I measured 5.5m between sink and box and the rod is 5, not sure if I have only pushed the blockage further.Boiling water did go down to a point before overflowing, but it was still gurgling, which is new. I will re-rod tomorrow and fish, then try some more water, failing this I could get a longer rod. I'll read up on the vent stack as can't say i've heard/read about this before. Many thanks for the response. – The Humble Rat Aug 19 at 19:09
  • Where is the vent in relation to the washing machine? – Greg Nickoloff Aug 19 at 20:22
  • are you absolutely certain that the diagram is correct? – jsotola Aug 19 at 21:39
  • Try pouring a few drops of washing up liquid down the sink then a few seconds later some boiling water – SpacePhoenix Sep 23 at 3:11

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