Drains Advice Please

[Zooks]

Hi, Please could someone help me understand how our drainage works.
I have an old stone building converted to a bungalow in the 70's.
There is a 5 inlet chamber in my garden going to another single inlet chamber further down the garden and then on to the main sewer.
I have 2 toilets both separately connected directly to this chamber with no vents or air inlet valves anywhere in their runs from toilet to chamber.
I have kitchen sink waste water going to 1 inlet and bathroom basin waste to another.
The remaining inlet is connected to a soil pipe running inside my bathroom and up through the roof.
Hopefully I have described that so it makes some sense.

The toilets are short runs aprox 8ft each so I am assuming there are no vacuum issues when flushing and the soil pipe vent is there to vent sewer gasses etc direct from the first chamber. Is this how this type of system works?

Some time before our ownership someone has connected a separate shower to the soil pipe inlet and is using this as a drain. I need to move this pipe for a new bathroom and there no room for any of it to remain where it is currently. If my assumption on how the system works is correct can I fit a vent pipe to one of the toilet runs to vent the chamber that way?

Thanks for reading

 

[Madrab]

Yes - make it to atmosphere though, don't put an AAV on it.

 

[Zooks]

Yes - make it to atmosphere though, don't put an AAV on it.

Thanks Rob.
Another question if you don't mind. I understand I can drop the vent size down from 110mm to 89mm but no smaller but am I then allowed to run any part of the vent pipe above the soil pipe horizontally?

 

[Madrab]

Yes - as long as it's the dry section of the stack - only consideration with that though would be is if the vent is open to atmosphere, you would need to be careful about rainwater/condensation gathering in any horizontal section. You would always want to have a min fall on it and ideally have a rain guard on the top.

 

[Zooks]

Yes - as long as it's the dry section of the stack - only consideration with that though would be is if the vent is open to atmosphere, you would need to be careful about rainwater/condensation gathering in any horizontal section. You would always want to have a min fall on it and ideally have a rain guard on the top.

Thats a good point about rainwater. Hadn't thought of that. Thanks