New soil pipe queries - turns and vents

2 Jan 2019
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United Kingdom
I'm installing a new soil pipe from a new bathroom to connect to where the original pipe is under the old bathroom. The intention is for this to carry waste from the toilet, basin, shower and bath.

I will need to ask building control to come out and inspect but don't want them to be wasting their time if wrong or mine installing something which is wholly not acceptable ('m new to this)

The old system had an un-vented clay run from the toilet to inspection chamber (the vent comes off another branch in the chamber) and i'm looking to connect to this clay pipe and carry it on to the other side of the house.

There will need to be a few turns in it which is a worry for rodding purposes as i don't want to have to have a hatch in the house to get to it. I know that the regs state that any change in gradient should be roddable. I should be able to make it just three 45's in the main pipe but also a branch here or there. Do BC say that a 45 bend is roddable?

Venting...A few choices with this idea for the layout.

1. leave it un-vented and let the other branch off the IC be the vent?
2. Put an AAV behind the toilet (under the stairs behind a stud wall with access)
3. Run a further pipe with the other side of the Y branch outside to give a proper vent outside.

I'd rather 1 or 2 to avoid having the visible vent on this side of the house but not sure what I will need?

Attaching a couple of drawings to help show what i'm talking about (hopefully)...

Does this look like something viable?

Thanks for any help


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What plane are the bends in? (Not sure from your picture.) Vertical you may just get away with it, horizontal, then very unlikely BCO will permit it. Drain runs should be straight, bends are permissible immediately outside a chamber, but 45's midway along a run are only going to invite trouble.
Thanks for the reply. The 45 closest to the toilet would be a horizontal (with correct fall). The other 2 are to change the vertical clay pipe to a new horizontal run, rather than having a 90 bend (which would be easier!).

Would the Y branch be permitted? Just considering what if any other options i have without putting the toilet in a different position
You can chance it, (whether the BCO will allow or not is another matter), but bear in mind, if it does block, how are you going to access it to unblock it?
Any way you could run in a straight line from the existing position you want to connect to, across to the proposed new WC position?

Either way, I'd be looking at putting an AAV on the end of the run at an absolute minimum.
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I was going to put access either at the toilet vertical stack bit (through the dashed AAV port in the pic) or further along outside the building (far left of the drawing). The AAV port would have to go around two 45's to get to the 45 under the bathroom (a 45 then through the Y branch) and outside could be a straight run to it.

The two 45's which are next to the clay>pvc connection could either be rodded from the same new access or from the inspection chamber (however the rod would need to go round the rest bend in the clay before getting to them.

Are either of these possible? I'm not clued up on how flexible rods are (or how flexible in the BC's eyes).

There is possibility to put an access 90 in above the clay, but it would leave me with a 90 rather than, what i've read, favourable twin 45's and also a need for an access through the floor of my living space.
I’d say the junction is the worst bit of the drawing.

If I were called out to unblock that i’d hope to be able to cctv and jet round the 45’s if the manhole isn’t too far away.
Rods may struggle to get round any bend sharper than about 20deg to be honest, I'd be reluctant to force them round for fear of getting stuck, or leaving some behind, especially with a corkscrew on the end. A jetting hose would go up there without an issue, but I'd be worried in case any forward pressure causes a blowback from the WC.

Its one of those things, 4" pipework is always superior to a macerator, and even with a convoluted run like you propose, installed properly with a sensible fall, may happily work for years to come without an issue. The fun starts when and if it does block, and you need to try and clear it without destroying the place in the process.

I certainly wouldn't carry a dry run on past the WC connection, end the horizontal run with a bend and come up to the pan and an AAV, the last thing you need is a 'dry' section where solid matter could accumulate.
This is all a bit disappointing!

How are the bends below pretty much all toilets acceptable then? Are the toilets 'removable appliances' giving direct access to the 90 below them?

The two 45's at the clay end of the system are a necessity without big work to go under the house/make a new trench around the outside of the house (with extra 90 degree bends and access hatches).

Ian, did you mean the junction from clay > PVC? There is rodding access from the garden around 4m away from this junction in the inspection chamber
Maybe an access 90 degree bend would be my best bet in the living space on the PVC>Clay connector?
Most toilets are removeable, but very rare you need to access the bend below, as it is very unlikely to block at that point. Bends in the horizontal section are an issue as they provide pinch points where blockages can build and are difficult to get rods around, which is precisely why the regs dont allow them.

To be honest, if you can route a new drain around the outside of the building, then this is going to be far more preferable to the BCO I think than running a drain under the floor with various bends in it. Should the worst happen and it block, cleaning it isn't a pleasant job at the best of times, never mind in the middle of the living room floor.
By junction I meant the Y under the toilet. If you were keeping that i’d lay it flat and put a 90bend into it pointing up.

Any chance you could go straight through the wall and have a small stack?

Either way, I don’t think it would block and it would be easy enough to unblock. I personally wouldn’t get building control involved, i’d save the money.
Hugh, i'll have a look whether not using a 45 in the horizontal section is possible. Making a new system around the outside of the house is a lot more work as it would be in the concrete driveway. Why would laying the Y down and using a 90 be good? Just better flow? I'll only need that Y branch if i needed it to carry on to provide a vent stack up the other branch of the Y.

Ian, it might be that i can go as you have drawn - it may mean I can't have the behind the toilet pipework behind the stud wall as succinctly though. I could have a 92 branch at the clay pipe end with access cap on top... i thought it would be beneficial to use a 90 bend instead for flow but maybe not?
Laying the Y down rather than pointing it up will help the water and solids flow in the right direction rather than them
just dropping into the pipe from above.

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