My mother's flat-roofed 5 story building has a small interior patio with bedroom windows. The interior patio also has a vent stack that comes up from the ground floor. The stack pipe has been cut off at the level of the 1 metre wall that surrounds and protects the interior patio on the roof.

When my mother opens the window that opens into the patio, there is a sewage smell. I presume that the denser sewage air sinks down into the patio well.

I would like to put a couple of 90º sweeps to make a 180 bend over the patio wall and then a short piece of pipe downwards, say 50 cm, so that the sewage air will emanate below the level of the patio wall and hopefully be "taken away" by breezes or diluted and not go back down the patio well.

My question is, will the 180º bend and the short downpipe affect the main vent stack's functions: allow air to enter to prevent negative pressures and to allow sewage smells to go out.

Thanks, George Marsden (e-maill removed)

Hi George

Plumbing code deals with this exact issue quite specifically by requiring vents in these circumstances to be run UP, above the highest wall that surrounds this pipe.

Here, as unsightly as it might sound, this pipe needs to be run up above and be hung properly. The pipe can be painted or camouflaged by climbing plants or other things (or can act as a flag pole, etc.), but the correct answer is NOT to turn it back down on itself... needs to be run above the windows and/or wall for best/healthiest result!

Hope that helped!

Mark