40mm pipe to 110mm pipe opposite sides of single storey building

[PlumbBob]

Hi

I am looking to install a shower one side and the toilet the other, so I need to join the two wastes together. It is best to extend the 110mm to the outflow of the 40mm and join up there with a 40/110mm adaptor?

Does it matter where the stub stack with AAV will be - assuming I just need the one (presumably on the side that means it is less visually intrusive which will be the shower side).

It needs to flow to a septic/wastewater tank (not installed yet)

 

[Hugh Jaleak]

How wide is the building? Regs limit you to max 3m run of 40mm, so you would probably be bets to run 110mm to a suitable point, (underfloor?), and drop into that with the 40mm.

Is there an open vent elsewhere on the drainage system?

 

[PlumbBob]

Hi, yes its more than 3m so I will drop into 110mm as it goes underground (this is all external grassed area) and go around to join up the stub-stack.

For the open vent I was intending to install the stub-stack with an AAV (sited behind the toilet)

 

[Hugh Jaleak]

That is my point, an AAV is an 'Air Admittance Valve', it will let air in, but wont let any positive pressure out.

Septic tanks need to breathe, if you effectively seal the system with an AAV, any pressure build up will look for the easy way out. Have know one blow back via a WC, the result wasn't pretty. I spent the rest of that morning fitting a vent on the pipework...

 

[Madrab]

For the open vent I was intending to install the stub-stack with an AAV (sited behind the toilet)

AS @Hugh Jaleak mentions, you need an open vent, an AAV isn't an open vent, it's a one way valve. Usually you would vent the main soil pipe by taking it up and out over the gutter line of your roof ( just so the smells don't invade your space) run either internally or externally.

 

[lostinthelight]

Septic tank gas can be explosive so if can't vent freely to outside then any escape inside could be nasty.

 

[PlumbBob]

Ah okay, I could have saved some money with the AAV.

The septic tank is an old style concrete thing with flags over the top, so well ventilated.

 

[lostinthelight]

Ah okay, I could have saved some money with the AAV.

The septic tank is an old style concrete thing with flags over the top, so well ventilated.

Are the flags over the whole of the tank or are there two chambers with flags over the second which is how I built a few in the 70's?
First chamber was holding and had concrete top, the second which was filled with filter medium had flags on top for aerobic treatment?

 

[Hugh Jaleak]

The septic tank is an old style concrete thing with flags over the top, so well ventilated.

It is at the moment, until the EA decide they dont like it and make you change it for a modern unit....

 

[PlumbBob]

@lo

Are the flags over the whole of the tank or are there two chambers with flags over the second which is how I built a few in the 70's?
First chamber was holding and had concrete top, the second which was filled with filter medium had flags on top for aerobic treatment?

its flags over the whole lot, with two chambers - so sounds like the ones you have built previous. Yes it is old but doesn't output into a stream/ditch so compliant with 2020 regs (despite what I am being told by salesmen of waste water treatment plants)

 

[lostinthelight]

@lo


its flags over the whole lot, with two chambers - so sounds like the ones you have built previous. Yes it is old but doesn't output into a stream/ditch so compliant with 2020 regs (despite what I am being told by salesmen of waste water treatment plants)

Building inspector of the time wouldnt allow flags over the first chamber it had to be concreted over with inspection cover and one way vent to let air in to carry gasses up the soil pipe. I suppose flags weren't considered safe enough given there was a 7 drop into 6 foot of effluent beneath them.Yours must be quite early or not quite so keen a BI.

 

[Hugh Jaleak]

Went to empty one once, lady gave me directions to it's location in the garden. I couldn't find it, turned out I was standing on top of it. Some of the slabs had fallen in, so it had asbestos roofing sheets laid over the gaps, and the whole lot was covered in leaves. I was standing on one of those sheets it aspired, was absolute sheer luck I didn't go straight through it!

 

[lostinthelight]

 

[PlumbBob]

Yeah it’s not ideal and may have to put a barrier around it.