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Kitchen sink waste drains slow - outside pipes under water -

Discussion in 'Plumbing and Central Heating' started by jdmorrisn, 25 Sep 2010.

  1. jdmorrisn


    26 Jun 2006
    Thanks Received:
    United Kingdom
    I have a twin bowl kitchen sink with U bend (previously tried to change it with s bend and bottle trap but same result), The dishwasher is attached to the waste via the spigot on the trap set up. the flexible pipe from the dishwasher is set up exactly as it should be and a high up swan neck. All waste pipes have a good slope- 30 -40 degrees.

    Now I will explain that I have a septic tank outside that drains off into the soil. But this tank was placed to low below the water table and so this means the tank itself is full all the time, draining out of the top and that the waste pipes from the house to the tank are always full (apart from each year when we empty it) but it fills again with ground water within a week. We have had this set up for 3 years - I am not going to fix this and dig it all up because a centralised system will be installed next year. Toilet, bathroom sink and bath are all with the same system but the water nicely drains from all these.

    But recently the kitchen sink pipes had a blockage, that was cleared (by emptying the septic tank) but now every time we use the dishwasher it just fills the sink. I have to pump away the water manually (which is fun) to empty the pipes, once the sink is empty of water you can hear the air glug, glug, glugging as the water goes away. But as soon as the dishwasher goes back on it fills up the sink again. If we don't use the dshwasher, I can run the tap all day and the sink empties quickly with no back up.

    So, not an ideal set up, but it worked before for 3 years but now doesn't. I know the problem is that the exit pipes are constantly full of waste water, but I can't change this. And like I said, it worked well until the blockage.

    Any ideas what I can do to help the water drain again?
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  3. Beerlover


    7 Sep 2010
    Thanks Received:
    United Kingdom
    All waste and soil pipes have to be ventilated- ie they have to be able to carry and refill with air. If this is not possible, you get what is known as double trapping. A trap with a AAV or anti-syphon trap will help; but this is only disguising the fact that your drainage is wrong
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