Cloakroom WC drainage plan

[swilli88]

The background:

• installing understairs WC
• wall is adjoining neighbours so drainage to run out to other side of house (about 4.5m to external wall, 6m to 4" stack)
• hanging sink with this trap https://www.victorianplumbing.co.uk/round-modern-chrome-basin-bottle-trap-tube-to-floor-pipe-set
• Attached screenshot of proposed 4" run route. total 6.1 m to vertical stack with vent
• Floor to external wall is concrete
• Adequate room for fall (see image)
  
• No room in WC space to build a false wall for basin waste and to avoid unnecessary joints in the ground, reducing basin gurgling (by joining to the 4" toilet waste) the plan is to step up the basin waste to a 40/50mm and run it seperately out to the stack, to prevent siphoning or possible blockage down the line.

Thought and advice sought please and thank you!

• I have
  

 

[sircerebus666]

https://www.toolstation.com/viva-90...btEIXDJTQaUze48UWzOkoU1m-C_v9WlwaAuKuEALw_wcB


You're only installing a basin one of these will be fine

 

[swilli88]

https://www.toolstation.com/viva-90...btEIXDJTQaUze48UWzOkoU1m-C_v9WlwaAuKuEALw_wcB


You're only installing a basin one of these will be fine

So i thought about that for sure but i already am very tight for space on the width of this bathroom so cannot afford the space a fase wall would take to hide a 32mm waster pipe.

Plan is to either step up 32mm to a 50mm and run it all the way out to the stack alongside the 4" or tee in the basin waste to the 4" at the 30degree bend in 4" that you see there. Which would you go for?

 

[sircerebus666]

Out of those choices I would just tee into 4" waste in the cloakroom , there's no point running another pipe outside especially an oversized one like you plan too for a basin which will only be used to wash your hands therefore using very little water

 

[swilli88]

Out of those choices I would just tee into 4" waste in the cloakroom , there's no point running another pipe outside especially an oversized one like you plan too for a basin which will only be used to wash your hands therefore using very little water

thanks a mill for your input. My only concern with teeing it into the 4" pipe with a rubber bung reducer or similar is that when the toilet is flushed and flows through the junction might it pull/siphon the bottle trap under the sink? i was hoping to get away without having a durgo on the back of the toilet

 

[sircerebus666]

Just use an anti vac trap

 

[swilli88]

Just use an anti vac trap

another issue there is that bathroom design (driven by higher powers...the missus) includes a chrome bottle trap so an anti vac plastic trap is out of the questions.

do you think the problem I mentioned is possible that the toilet flush pulls vacuum on basin trap?

what about putting a 32mm air admittance valves on the pan connector? Would that solve it?

 

[Hugh Jaleak]

Right on the cusp of whats allowed with a 6.1m 110mm run from the WC, but that length of run for a waste is asking for issues I'm afraid, you will be better coupling it in to the WC run. Less chance of the WC run pulling the basin trap than using a separate waste run over that distance, even if using bigger diameter pipework.

I'd be tempted to see what happens, if you find the basin trap is being pulled, look at fitting an AAV on the basin run somewhere, but you may well find there is no need.

 

[swilli88]

@Hugh Jaleak nearly word for word that's what a plumbing friend of mine suggested! thanks for your input!

what would you suggest as the best parts to use to tee in the 32mm to the 110mm? rubber bung reducer? straight into the 110mm Y junction or add a small length of straight 110mm to the Y first and reduce down to the 32mm a small distance from the junction. Might reduce the chances of a pull on the basin trap if you have a small length of 110mm run between the Y and the basin? does this make sense or is it pure waffle?

 

[Hugh Jaleak]

I'd personally look to connect the 32mm in as near to the WC as possible, (also looks neater), the pan connectors are made with a 32mm boss for that reason.

I wouldn't be running any 110mm upstream horizontally from the point where the WC connects, it's asking for possible backflow and/or build up of soil, with insufficient flow from the basin to wash it away again. Otherwise WC run in this situation isn't much different to an underground drain run from the WC, (which can be more or less any length you like within reason), like any drain, if laid correctly and the WC isn't used as a dustbin, should never give an issue.

 

[swilli88]

https://www.victorianplumbing.co.uk/round-modern-chrome-basin-bottle-trap-tube-to-floor-pipe-set

so this is why i cant connect the basin waste to the boss on a pan connector. cloakroom not wide enough to allow me to build a false wall to hide waste pipe in the wall and missus wont go for surface mounted waste pipe the full length of the wall. So the waste needs to go into the floor. How would you tee in the 32 to 110 underground where that issue you mentioned could be mitigated against? the junction would be roughly where the 30 degree bend is in the attached image

 

[JimCrow]

A 110mm branch across then a 110mm bend looking up to the centre of where the basin waste is, then one of these reducers at floor level.

 

[swilli88]

thanks @JimCrow, yes iv seen them in my search!

do you think there would be any risk of the issue @Hugh Jaleak mentioned? backflow and soil build up?

I'd personally look to connect the 32mm in as near to the WC as possible, (also looks neater), the pan connectors are made with a 32mm boss for that reason.

I wouldn't be running any 110mm upstream horizontally from the point where the WC connects, it's asking for possible backflow and/or build up of soil, with insufficient flow from the basin to wash it away again. Otherwise WC run in this situation isn't much different to an underground drain run from the WC, (which can be more or less any length you like within reason), like any drain, if laid correctly and the WC isn't used as a dustbin, should never give an issue.

 

[Hugh Jaleak]

Ok, I see your difficulty! Fit the junction as near to the WC as you can, and ensure you have adequate fall on both sections of drain to the junction. Provided the WC flush washes any solid matter past the junction you should be ok.

 

[swilli88]

ok @Hugh Jaleak I will try to get the junction as close to the WC as possible if i go that route.

1. do you think from my sketch attached if the proposed junction location is close enough or do you suggest trying closer? About 1m meter into the 110 mm run.

2. The other thing I might reinvestigate today is to build a small false wall to hide the 32mm waste and bring it to the back of the toilet to connect to the toilet pan with 32mm connection. As it stands, without the false wall, I will have width of the cloakroom toilet of 800mm (suggested minimum from what iv read). On the solid wall joining us to our neighbors now is a sheet of plasterboard with dot and dab. If I pulled the existing board and mortar off the wall and built a slim stud wall directly onto the brickwork as shallow as possible to hide the 32mm pipework then I may only lose about 30-40mm on the width of the WC (when you consider the void created by dot and dab). What do you think? It would also provide space to run the running water more easily and remove a major sewage junction under concrete. the only downside is a bathroom width of about 750mm in the end

its worth noting also that i intend to put wood panelling on lower half of WC wall so i can include the thickness of the plasterboard beneath as depth available to hide the pipe. I would basically plan to pull back the 25mm thick current finish (dabs and plasterboard) to the brickwork then build a 50mm or so studwall onto the brick. Then I would chase out the plasterboard and studs to accommodate the 32mm waste, which would be about flush with the surface of the plasterboard. Then the wood panelling finish covers the lot up. Am I making sense? might seem like overkill but really just want to maximise the size of the WC.