Shower trap syphoning...

[MattChan]

The basin and shower are connected on the same 40mm pipe that runs to the waste stack in the bathroom.

Starting from the stack there is a 3m run of 40mm pipe, then a T directly below the basin where the 32mm waste from the basin joins then 1m of 40mm pipe to the shower.

If the sink is filled up and then allowed to drain the shower trap is syphoned out and the seal is broken.

It looks to be bloody difficult and destructive to get to the 1m of pipe between the shower and basin to fit an air admittance valve (the rest of the run to the stack is accessible) and changing the shower waste to an anti syphon type won't be a trivial task either.

I'm pretty sure these are my only two options but I thought I would see if anyone had any ideas before I start destroying things to sort it out?

 

[seco services]

is the basin waste an anti vac trap

 

[MattChan]

nope the basin waste is a standard 32mm trap like this kinda thing:

 

[cb9002]

Then hopefully changing the basin waste to a HepVO trap would sort it.

 

[MattChan]

How does that fix it then? Does it mix air in with the water coming down from the sink?

 

[MattChan]

I swung by wickes and bought a "hunter plastics gurglemaster II" basically its an in line air admittance valve:

I put this in line with the existing sink trap as the hepvo doesnt fit within the semi pedestal on the sink. Much to my surprise it seems to work

 

[Gasguru]

Just check the air admittance valve on a regular basis...they are prone to leakage and you first know when it's marked the ceiling below. Of course if the shower trap wasn't bodged by the installer (probably only an 18mm seal) you wouldn't have the problem.

 

[MattChan]

I don't think the seal can be that big as its this type of waste:

I can probably manage to change the waste on the shower looking at it. Whats the best type of waste to go for on it?

 

[Gasguru]

Top access shower trap with 80mm seal from McAlpine http://www.mcalpineplumbing.com/index.asp read the FAQs on their site.