soil pipe and bathroom waste design

3 Jan 2013
Reaction score
United Kingdom
Hi all,

I am trying to design a waste system for a new ground floor bathroom with a concrete floor. The property is in rural france so building regs will not really apply as it won't be inspected, but i obviously want to do it right and safely.

The bathroom will have a bath to the right, a sink in the centre and a toilet to the left. To the left of the toilet will be a stud wall behind which will be a large cupboard housing the soil stack and a washing machine.

With regards to the soil stack i envisage a 90 or 92.5 degree access branch to accept the outflow from the toilet. The soil stack will go below this through the concrete floor into a cellar and then through the rear wall via a curved 90 degree access bend and then via an inspection chamber into a septic tank i am having installed.

The vent for the stack will be up through the ceiling into the loft space. Can i terminate it here with an air admittance valve or will i have to take it through the roof to vent?

The bath will have a 40mm waste pipe running just above the floor from it to behind the basin where a 32mm waste will join into it. As this waste run will be more than 5 feet, i intend to run a vent pipe vertically from it between the bath and sink and then horizontally to join the soil vent pipe via a strap on boss.

I am struggling though, as to how to feed this waste from the bath and basin into the soil stack. It will be a bit of a squeeze to fit it to the soil stack via a boss at the same ,level as the toilet waste, so i am thinking to run vertically down into the cellar and accross to join the soil stack below the toilet waste and do the same from the other side for the washing machine waste. I would connect them to the soil stack either with a boss pipe connection or a manifold.

Can i have any feedback on whether this all sounds ok, and if not, where am i going wrong and do you have any better suggestions. Thanks.

Sponsored Links
It all sounds as if it will work but I wouldn't join the basin (sinks are in kitchens!) waste to the bath waste - run it as a separate waste to the stack or join to the bath waste in the cellar (ie below bath level). Use anti-vac traps on both bath and basin wastes to prevent the traps siphoning.
Thanks for that, so that will negate the need for a vent pipe from the bath/basin wastes as the antivac does the same job?
also what are your thoughts regarding the stack terminating in the loft with an air admittance valve rather than having to punch through the tiled roof?

I'd be inclined to vent - although I don't know the requirements (legal or practical) for septic tanks but instinct tells me to open vent
Sponsored Links
Personally would put an external AAV at the tank end, and open vent at the house end. Air passing over the vent should put a slight negative pressure within the system, allowing air in via the AAV and ventilating the system. Can get a build up of gas in a septic tank, better to try and vent it out if possible.

The septic system will be vented as part of the installation. My problem with an external vent rather than an AAV for the soil stack is that there is an external dormer type entry to the loft above where the soil stack will be sited which may become a window if i convert the loft in the future. I can re jig an internal AAV to avoid it, but having an external vent will be tricky to by pass it and get the vent high enough neatly to avoid problems if it was to be converted into an opening window.

You may be able to reduce the vent section to 82 or even 50mm if that would help. Main problem with septic tanks is they can produce Hydrogen Sulphide, thoroughly unpleasant stuff, highly toxic and will rot away metal and concrete!
Can someone help how do you connect a basin waste into the top of a soil pipe as there isn't enough space to fit a boss on the side
Can someone help how do you connect a basin waste into the top of a soil pipe as there isn't enough space to fit a boss on the side
Now where did I leave that crystal ball???....what a stupid fookin question..jeez..
Let me guess what you had for breakfast this morning...
Last edited:

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links