slow draining kitchen sink

22 Jan 2004
Reaction score
United Kingdom
Hi, I've got a VERY slow draining kitchen sink !!!

To set the scene, the sink has a standard U-bend trap which then runs horizontally to a vertical down pipe. Approx. 18 inches below this another U-bend trap directly under the sink - the washing machine and dishwasher both empty into this through a one way valve - also enters this vertical down pipe which then flows out to the main 6 inch diameter waste. The down pipe that both these drain into has a screw cap on top level with the bottom of the sink.

The symptoms are that although the sink has always been rather slow to drain it has now taken to draining even slower. The waste from the washing machine and dishwasher are now tending to flow back up into the sink too.

I've put a considerable amount of caustic sink cleaners down the sink and after no joy, I've removed the cap from the vertical pipe and sent some down that too. I've also removed a large chunk of limescale build up from the sink U-bend. None of this has had anything but a minor effect.

When draining the sink I've found that if I unscrew the cap, there's a rush of air and the sink drains very quickly until the 'water' fills the vertical pipe and I have to replace the cap or flood the kitchen!

This all leads me to believe that there is a considerable blockage in the pipe connecting the joint kitchen waste to the main sewer line, as the toilet and bath on the floor above both have no problem draining to the same main sewer line. The line from the kitchen waste to the main sewer pipe is around 4 metres.

What to do next please?

many thanks . . . evan p
Sponsored Links
You've obviously got a blockage or incorrect gradient on your waste pipe.
Disconnect all your wastes and inspect and clean out thoroughly.
If all clear and problem still there you need to look at your soil pipe for any blockages. :p
I just noticed you said you have a 4 metre run of waste pipe. :oops:
Max recommended length is 3 metres so you will have to fit an air admittance valve within 150 mm of your sink trap.
Ask your plumbers merchant for advice ;)
Thanks Bahco !

It's strange that I haven't had any problems for the last 18 months I've been here - and the piping isn't new except for the addition of the dishwasher waste. Maybe it's food goo build up over time . . . Could I run a wire or similar down the pipes as they are boxed in and I'd like to avoid the carpentry thing . . . ?

I take it an air admittance valve is a one way valve I could exchange the 'cap' for. There is an overflow attached to the sink which would allow the air to escape from the sinks U-bend.

thanks for your help !!!
Sponsored Links
Clean you sink all away. Been doing that lately to my problem too. =D

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local