Siphoning?

[amason79]

Hi, I need to divert a 32 mm waste pipe (from a basin) into a 40mm waste pipe (from a bath), but I am worried that when the bath is emptied that the water in the basin trap might be siphoned out and that I will get foul air traveling up the 32mm pipe.

Is this likely, I would be Tee(ing) the 32mm pipe into the 40mm pipe approximately a metre from the bath?

 

[Softus]

It is not likely to syphon if you have a bath overflow, because this acts as a vent.

 

[Nige F]

And it won`t syphon at all, or allow back flow of smells.if you fit a Hep2-o waste valve to the basin

 

[Softus]

Nice one NF! I haven't ever tried one of those - are they good, and do you find many cases where they're justified?

 

[ChrisR]

They're expensive and you have to find somewhere to put them though. Why not just use the normal solution, a trap on the basin with a built in AIR ADMITTANCE VALVE - see definitions.

 

[Nige F]

Granted, they`re expensive but the same size as a straight through trap. I`ve used the mini a.a.v`s too, Both things I have fitted as a prophylactic measure....that and swept bends are my favourite specs. for waste pipes. I personaly think Hep2o`s valves are a brilliant idea........eg. to fit in place of basin trap requires 2x135 degree bends to alter pipe centre line.........OK you can`t use one if the pipe goes thru the wall horiz. from trap. But you can use them as a running trap.