Vent pipe for bathroom to stop septic tank stink

Hi,

Long story short the bathroom in holiday home on the Western Isles of Scotland has no vent pipe after an extension was built. Depending on which way the wind blows the smell from the septic tank is not pleasant to say the least.

The extension was built on the back wall of house which had the bathroom and the original vent pipe was attached to the external wall of the house. Looking at fitting a vent pipe but the question is how far from the bathroom can the vent pipe be and still do it job?

My plan is to dig down to the clay waste pipe that runs to the septic tank from the bathroom, cut a section out, replace with a PVC length of around 1000mm, add a vertical vent pipe that can then be attached to the outside wall of the new extension. The closet I can dig down and attach the vent pipe to the waste pipe from the bathroom is approx 3.5m, will this be ok?

 

Ideally the vent should be at the head of the drain run, but as near as possible will be adequate. I'd also look at fitting an external grade Air Admittance Valve on the sewer, just before it enters the septic tank. This should allow some circulation of air through the drainage system, and thus vent off smells and gases from the vent pipe and out of harms way.

 

Where I am planning on putting the vent is only 4m from the septic tank, is it still worth fitting an Air Admittance Valve on this short distance? If it is then I will take your advice and fit one.

Also the septic tank is an old concrete one covered with 3 heavy concrete slabs that have about 10mm gaps between then meaning the tank is not fully sealed. Should the cover of the septic tank be sealed up?

 

Cover of the tank doesn't need to be sealed, unless odours are an issue. If it's not airtight then that could be a bonus as it'll allow air in to pass through the system and do the job of an AAV for you. Otherwise is smells remain an issue, then I'd look at sealing the tank and fitting an AAV.

Basically you want the odours to be drawn out via the vent and dispersed at a higher level where they are no longer offensive to people in and around the property. Air passing over the vent will create a negative pressure in the system, its a question of how best to allow fresh air in at the other end.

 

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