Siphoning

[andymason79]

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

[Andrew Gabriel]

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.