WC Soil Piping needs sorting :-(

[advisewelcome]

H there, welcome any advice.

Moved a WC from the garage to the under the stairs room...

This was the old WC in the garage room...

The garage room now just has a soil stack going through to the under stairs room...

The garage room is a 22cm step down from the rest of the kitchen & house...

This is the under the stairs room with the new WC soil piping coming above the floor to the new WC...

The 110mm piping comes through the wall and connects to the new WC with a pan connector...

But...

The soil stack is too high in the garage room...

We want to put a floor in the garage room flush with the kitchen floor (22cm high) and put a shower there. Be nice to have the shower on a low pedestal.

Am thinking this would be the solution:
-Put a new lower floor drain connector in the garage (link to DC90 connector)
-110mm piping under the quarry tiled floor
-Then elbowing up to the WC

Queries...

-Not sure what's the best garage floor connection (dc90) or are there alternatives?
-Should I use a swept elbow up to the WC as not sure if it will fit - or can I use a 110mm knuckle elbow?
-What should I put on the pantry floor where the pipe comes up (or just leave a bit of110mm pipe cut flush with the quarry tiles)?

-I aiming to connect future shower 50mm wastes and 50mm sink wastes to the 110mm piping at a later date

Any direction (or things to watch out for) very gratefully received as need to crack on with it this weekend

 

[Scally-Ho]

I would not recommend such a tight knuckle elbow for a soil pipe connection. It will be a bit of a faff, but IMO the correct way to sort that new height pan connection to your new desired lower point, is to dig up the floor to expose the soil drop and then work your way back up from there. Other connections can then be accommodated before your desired finished floor level. The last effect you want is the shower trap seal lost every time that pan is flushed.

 

[yorksbuilder]

Isn't there hundreds of posts about this installation already?

 

[CountryFan]

Maybe you could use a couple of 30 or 45 degree bends to offset the pipe to the next room?

 

[advisewelcome]

I would not recommend such a tight knuckle elbow for a soil pipe connection. It will be a bit of a faff, but IMO the correct way to sort that new height pan connection to your new desired lower point, is to dig up the floor to expose the soil drop and then work your way back up from there. Other connections can then be accommodated before your desired finished floor level. The last effect you want is the shower trap seal lost every time that pan is flushed.

Thanks for reply. I think your saying that the DC90 drain connector is too much of a sharp bend and risks blockages?

Digging up the garage floor and attaching to the clay pipe lower down is really is going to be a massive faff and I assume raises all sorts of risks if that piping (probs clay piping in old 1940's house) get damaged.

Not sure there is swept-bend-drain-connector around that would fit under a new 22cm floor height? I could try and avoid 110mm knuckle bends coming up to the actual WC pan in the next room, if possible.

Would putting the shower on a bit of pedestal prevent any shower trap issues (would be a smaller pedestal than the massive one required now)?

Plan was to fit the shower wastes and future sink wastes with strap on connectors or insert this connector into that long 110mm pipe - so some flexibility on the 50mm waste piping location in the future.

 

[endecotp]

Back in your original thread about this in August 2024, in post #4, @denso13 told you that “You'll need to dig down and make a connection to keep everything below floor level”. That’s still what you’re being told now, e.g. by @Scally-Ho above.

 

[advisewelcome]

Back in your original thread about this in August 2024, in post #4, @denso13 told you that “You'll need to dig down and make a connection to keep everything below floor level”. That’s still what you’re being told now, e.g. by @Scally-Ho above.

Thanks. May have lost track of older threads.

Can anyone provide any brief overview of what is required to do that - any special tools or connectors needed and risks involved? Will help me assess the possibilities of doing it.

I assume its digging up the concrete garage floor, somehow making a connection to the old clay piping - with the serious risk of cracking it? How would the connection arise out of new WC room tile quarry floor? - should some sort of end connection be flush with the quarry tiles so that a pan connector can plug into it?

 

[Scally-Ho]

T

Would putting the shower on a bit of pedestal prevent any shower trap issues (would be a smaller pedestal than the massive one required now)?

Plan was to fit the shower wastes and future sink wastes with strap on connectors or insert this connector into that long 110mm pipe - so some flexibility on the 50mm waste piping location in the future.

Your problem with the proposed shower waste will be caused by the vacuum induced every time the WC is flushed, because it will not be vented to the atmosphere. That vacuum will suck out the trap water seal and in turn give any accumulated 'sewer gasses' free access to your new shower room .. nice and niffy!

Anyway, I'm done here because I'm fed up with offering free advice gained from over 60yrs experience only for it to be ignored.
You do what you want and then see what the area building inspector has to say and he writes out a prohibited notice.

 

[advisewelcome]

Your problem with the proposed shower waste will be caused by the vacuum induced every time the WC is flushed, because it will not be vented to the atmosphere. That vacuum will suck out the trap water seal and in turn give any accumulated 'sewer gasses' free access to your new shower room .. nice and niffy!

Anyway, I'm done here because I'm fed up with offering free advice gained from over 60yrs experience only for it to be ignored.
You do what you want and then see what the area building inspector has to say and he writes out a prohibited notice.

Thanks. Expert indignation aside, there are some valid points that I am listening too.

There is one plumber chap that I trust with doing this work and he his not available until next year so have to look for workable options as need something sooner.

1. WC soil fixings
I think you realise our requirement isn't to keep below the current concrete garage floor (unless its not possible to avoid future issues). The requirement is to just keep it underneath a new 220mm stud garage floor. If there is workable elbow that connects to the current garage drain and can keep soil piping below a 220mm - it will be worth a shot to see if it fit for purpose.

I am calculating that the below connector will have the 110mm pipe running to the new WC room at (118 + 55) 173cm high...

Surley McApline aren't producing fixings which are not fit for purpose and clog up? Although there does not "seem" to be a natural fall on this, I would prefer a swept bend drain connector that will fit under 220mm new floor height with the right fall (1:80?) to the WC. Not sure if such a product exists??


2. Future Shower Trap Waste and Sink Waste connections
The plan was to future connect into this 110mm pipe drain:
1. A small sink waste pipe from the new WC room (through the wall)
2. A sink waste for new sink in the garage shower room
3. Shower waste with the new shower tray (plug hole closer to the door entrance) sitting on top of the 220mm stud floor above the 110mm WC pipe

Is there a chance I can position the future waste connections into the 110mm pipe so that the sink wastes and shower wastes will work? Worse case can put the shower on a slight pedestal if needed, or add some products (dry traps, venting) to prevent vacuum issues highlighted?

 

[Hugh Jaleak]

Here is your previous thread. https://www.diynot.com/diy/threads/wc-into-understairs-pantry-nightmare.632920/

We spent five pages on that going round in circles as you weren't getting the answers you wanted. I'm out.

 

[advisewelcome]

Here is your previous thread. https://www.diynot.com/diy/threads/wc-into-understairs-pantry-nightmare.632920/

We spent five pages on that going round in circles as you weren't getting the answers you wanted. I'm out.

Thanks for that link as was trying to find it...

Hugh Jaleak "Replace Flexi with rigid pan connector, as per middle photo. Get rid of the offset pan connector joining the soil pipe to the bend. Use a double socket bend and sections of 110mm pipe as required."

...you can see I actually actioned the advice provided - nothing was said about "induced waste vacuums" and so in this pickle now.

There are challenges attaining local expert resources, I can't take too much risk as the WC can't be out of order for too long - thus have to make the best of it. Digging up a concrete garage floor where a clay pipe is, has got risk written all over it and thus the option of last resort. If I can lower the piping enough to run under a new 22cm stud wooded garage floor and it does not block or leak - it will be a win. To that end...


(1) DC90

Its finally arrived . I spoke to the tech manager within McAlpine earlier this week - he said that the DC90 was a "get out of jail" solution for these applications. He went on to say that its knuckle angle will work as long as there is min volume of 6 litres within the flush. I measured the Wicks WC and looks like the cistern holds 8,223 cm³ of water (8.2 litres) so it should work despite the lack of fall. A sensible plan would be to get it in, check it works, test it - and rollback out if problems start (by putting the old piping back). A simple option would then be exhausted before digging the concrete garage floor up.



(2) Induced Vacuums & AAV

This does look like an unforeseen issue. I am hearing that AAV's (air admittance valves) are the solution or even on the smaller basin in the WC room an anti-vac trap? I am pretty sure the McAlpine tech said something about them needing to be at the "head of the piping", and I read something about them needing to be 20cm above the water inlet into the WC? I am just trying to work out where a 110mm AAR can be placed by understanding them.

https://www.diydoctor.org.uk/projects/air_admittance_valves.htm

https://assets.publishing.service.gov.uk/media/5a80cf9ded915d74e33fc8ae/BR_PDF_AD_H_2015.pdf

Ideally would be great if an AAR can be fitted on the 110m piping section in the garage (the plan was to make a stud wall to hide garage shower piping) and wonder if it could be put there?

 

[advisewelcome]

Back in your original thread about this in August 2024, in post #4, @denso13 told you that “You'll need to dig down and make a connection to keep everything below floor level”. That’s still what you’re being told now, e.g. by @Scally-Ho above.

Think I have come to the conclusion that they may have had a point about digging up being the only option.

This is what we have at the moment...

I reckon I can get that white 110mm pipe down to the floor level and that will probably be good enough to get a shower 22cm above this floor (level with the kitchen floor). Just have to work out how to connect to the below piping.

Digging up I see this...

Looks like a plastic brown swept elbow soil pipe which the black connector plugs into...

Could I instead use this grey elbow and connect its grey spigot end to the brown elbow?...

It has a boss which I can connect the shower waste and sink waste. The boss would hopefully be at floor level which gives good clearance for falls. Something like the below...

(1) The current large soil stack which is 38cm high and 16cm above the stud floor which would be put in to be level to the kitchen floor. The shower pedestal would have large step onto it (26cm and above).

(2) The previous solution with the DC90 McAlpine connector which does not have a boss inlet, was still a bit too high to get strap on waste connectors on the 110mm pipe for shower and sinks and therefore would have minimum benefit.

(3) Suggested grey Elbow connection lower down onto the floor. This grey elbow has side inlet (hopefully can sit just above the floor) and be used for the sink and shower waste. A coupler would permit a 110mm pipe to run along the garage floor and into the adjacent floor underneath the quarry tiles and to up to the WC. I assume the grey elbow spigot end could not be above ground and as the 110mm end may not slot into the current under-the-ground brown elbow 110mm pipe?


...This sound like a plan and any other ideas for connecting to the brown plastic underground elbow?

 

[Hugh Jaleak]

I'll relent, and give my take on what to do, given you've now done what you were told to 12 months ago...

Dig some more out so you can run the 110mm across to the wall under the floor. The bend will need to be replaced anyway now, the seals will have hardened and it will leak if you try and reuse it. Remove enough material to expose around the bend, and remove it from the end of the horizontal run. Fit a Coupler and continue the pipe to the wall, before putting a new bend on the end to bring you upwards.

A short Boss Pipe in the bend coming up may get you the waste connection you need at the right height, then ideally from here, come up, fit a Junction to accept the WC from the other side of the wall, then come upwards a bit more from the junction and fit an AAV. This can be boxed in as required, fit a small vent in the boxing to allow airflow.

 

[advisewelcome]

Hi, good to hear from you and thanks for feedback.

Had confidence to dig it up as found plastic piping in the manhole outside to the downstairs WC.

I think I get what you are saying about the connections. Some quick queries...

1) Is the AAV necessary if there is only a 3.5m distance from manhole to the downstairs WC?

2) And would a smaller AAV (32mm, 40mm, 50mm) work instead if its a short run?

 

[advisewelcome]

Hi, if you're asking me to do as suggested, would welcome your kind engagement pls to ensure I understand the helpful suggestions.

Is this the plumbing part being suggested into the WC?...