I have this problem with my kitchen sink.
It is a one & one half bowl sink, which has a sink & waching machine connection 'S' bend pipe fitted.
The problem is that when we drain water from the half bowl sink, it immediately backflows into the main sink & takes ages to drain away. This drainage problem also happens with the main sink, where the water might drain away up to a point; where it then fills up again into the main sink & takes ages to drain away.
This problem also happens when we do washing. When the washing machine does its' spin cycle or refills with fresh water, the old water pushes up into the main sink and also takes ages to drain away. This obviously leaves us with a horrid smell in the house.
We have poured corrosive chemicals down the hatch to dissolve any grease or other matter, which did not solve the problem. I have disconnected all the pipes to check for any obstructions, but nothing.
We are at our witts end & don't know what else to do. With all of the drainage problems, there has also developed a foul smell coming from the outside drain. Unfortunately this is under the conservatory floor, which I am willing to lift it need be to solve the problem.
Doe anyone have a clue what to do about this? Do I change the connections to something else, do i fit addtional connections to the current pipes? Please help!!!