Septic tank ventilation

[Tipper]

Whilst clearing rubble and rubbish above my septic tank I have found a broken off 100mm pvc pipe stub which I asume was a vent into the septic tank. Is this what it is? The drainage from the tank appears to be solely by percolation through the tank walls according to the CCTV guy who did a survey for me.

The drainage system from the house includes a SVP which itself comes from the nearest manhole which is about 10m above the tank inlet on a steeply terraced site and rises another 3 floors above that to the house roof. Also included recently are 3 new drain branches which all terminate in an AAV located inside the property.

We've not had any problems with smells, yet, due to not fully using the system whilst renovating and converting the property. Do I need to reinstate the tank vent, if that's what it is, and does it need an AAV type of termination or similar in a safe position?

I've looked at various Klargester tank drawings online but although a vent is identified it gives no details which I could follow.

Any help much appreciated.

Edit: The new drains have all been approved by the BCO but no comment has ever been made about the septic tank. I assume this is because it is existing and privately owned.

 

[Tipper]

Anyone?

 

[Hugh Jaleak]

What type of tank is it?

 

[Tipper]

It's a great big concrete block lined hole in the ground with a concrete top.

 

[Hugh Jaleak]

I was wondering as the Klargester 'bottle' type tanks have 'dip tubes' that finish flush with the surface. In your case though I dont see any reason why you cant fit an AAV at the tank. Theoretically air passing over the SVP at roof level should put a slight negative pressure in the system. This could then draw air in the AAV at the tank and ventilate the system.

Most of the bacterial action in a septic tank should take place anaerobically if its working correctly anyway.

 

[Nige F]

sorry to disagree but I don`t think an aav will allow a natural draft in - it`s more for the "slugs" of air that move in s/v pipes when loos are flushed . Just put a baloon or rain cap on it - and save money Dip tubes are a sideways T with the top open to let air in and the dipped bit allows the crust to form and not be disturbed by inflow .