Hi, I need to divert a 32 mm waste pipe (from a basin) into a 40mm wast
pipe (from a bath), but I am worried that when the bath is emptied tha the water in the basin trap might be siphoned out and that I will ge foul air traveling up the 32mm pipe.
Is this likely, I would be Tee(ing) the 32mm pipe into the 40mm pip approximatley a metre from the bath
-- andymason79
Bath traps are often shallower because of lack of space, and it is thus more likely you will empty the bath trap first. If that doesn't already happen, then adding a basin waste isn't likely to make it do so. You can get basin traps with built-in air admittance valves for only a little bit extra money if you are worried, and that will also stop the glug-glug noises. I used one in the case of a condensing boiler condensate drain tee'd into the same pipework as a basin so the condensing boiler's U-trap couldn't get sucked dry after draining a basin full of water.
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