I have a double sink with the waste from each sharing the same pipe through the wall to the drainShould I fit an air valve to stop the syphone from the traps and if so should it be the furthest from the drain?
There is no specific need to fit an anti syphon trap unless you are experiencing problems with the water seal being broken. If you do decide to fit a air admittance valve, it should be sited at the highest point which will be the furthest point from the drain.
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