Venting Smelly septic tank- vents or AAV?

[SimonWr1]

Recently moved into a house with a septic tank and have a few issues with smells coming off it.

Tank is onion style and was emptied when we moved in 3 months ago.

The tank fills exremely quickly and appears to work okay with clear effluent visible in the drain field inspection chamber - gulley.

The tank has the old klargester diamond shaped cover with the main neck, inlet and outlet pipes visible in the cover frame.

The house is a bungalow approximately 30m long and AAV- Durgo valves are fitted on top of all soil pipes in the roof void, there is no atmospheric vent external to the house.

The below ground pipe travels 22m to the septic tank and there is no visible vent.

The smell comes and go's but seems to peek about every 4 weeks which usually coincides with a blockage in the tank end of the 22m long pipe.

I have a feeling that the problem is due to blocked sewer gasses blowing through the manhole lid.

How do i apply vents and how many, where, what size and what materials do i need?

 

[wastetech]

Durgo valves should not be used with septic tanks, only when the drains are connected to the mains. This is because the main sewers have pumping stations on the line which draw the air along with the sewage. Also, the septic tank requires a soil vent pipe to be fitted within 10 metres of the tank. Soil vent pipes can only draw up to a maximum of 10 metres, so your drain run of 22M is way too long to run it back to the house. They were not called 'STENCH' pipes for nothing as they draw the stench from the tank and drains and let it escape high enough to not cause a problem.
See smelly drains and septic tanks

 

[Hugh Jaleak]

Tank will fill quite quickly, remember every drop of water you use in the house goes into the tank. Principle of the tank is to allow the solids to settle and then the final effluent dissipate via the leachfield.

Never heard of the 10metre rule, there are runs a lot longer than that out there! I would suggest you work out where the highest point of the drain is, i.e. furthest point from the tank and alter the existing Durgo arrangement to an open vent through the roof. Then it may be prudent to fit a Durgo as close to the tank inlet as possible.

Theoretically then, air passing over the open vent will cause a negative pressure in the system, causing the Durgo at tank end to open and allow fresh air in, thus venting the system.

 

[SimonWr1]

My thoughts on this are that the venting of the tank is to mitigate the sewer gases created within the tank. I guess it would need a vent pipe of of the inlet or outlet pipe taken to a safe position and vented at say 2.5m above ground.

My understanding of AAV is that they are a one way valve to let air in - not smelly gasses out.

Can I fit a strap on boss to one of the pipes (below ground and take a 50mm vent to discharge?

Sealing the lids of manholes with grease will hold back the smell but eventually the buildup of pressure within the tank will burp out somewhere, either lifting a cover, bubbling through a trap seal inside the house or?


there are no openings in the roof ATM so I am loathe to break through the existing roof tile.

 

[Nige F]

vented at say 2.5m above ground.

too high .


there are no openings in the roof ATM so I am loathe to break through the existing roof tile.

Then you`ll have to live with the smell - inlet @ low level ( not a durgo ) open pipe with cage will do - same for pipe in roof , sealing slate through tiles , cage on pipe .

 

[SimonWr1]

vented at say 2.5m above ground.

too high .


there are no openings in the roof ATM so I am loathe to break through the existing roof tile.

Then you`ll have to live with the smell - inlet @ low level ( not a durgo ) open pipe with cage will do - same for pipe in roof , sealing slate through tiles , cage on pipe .

Can you please explain why the 2.5m high open vent by the tank will not expel the sewer gasses? Not questioning your suggestion but would like a reasoned statement.

Got no vents at the moment so i guess that the tank becomes positively pressurised as the sewer gasses form. a little concerned by this 10m statement too. the nearest durgo on a soil pipe is 25m from the tank while the furthest is about 55m?

 

[Hugh Jaleak]

Any vent should help, but the idea of venting through the roof is to expel the foul air at a point where it wont cause a nuisiance. Having a vent at a lower level near the tank and wind in wrong direction may result in your getting odours where you dont want them. (Useful maybe though if you have the outlaws staying! ) The other advantage of venting at the highest point of the drain will allow ventilation of the entire system.

I wouldn't worry about the distances, i've never heard of a 10m rule, the vast majority of main sewers are gravity flow. Pumps are only used where necessary.

 

[Nige F]

the pipe @ the tank inlet acts as an air inlet , the pipe in the roof should be open vented - so there is a flow of air from tank to roof . So it`s kind of traditional to have the inlet low to the ground - and it would look odd standing up . Fact is the setup is wrong and I`m sure the way to remedy is to revert it to the trad. setup rather than attempting to vent pressure built up because the durgo shouldn`t be there

 

[mysteryman]

AAV can be taken to mean Automatic Air Vent, or Air Admittance Valve. These do exactly the opposite thing; the first lets air out, the second only lets air in. With Durgo air admittance valves only, you can get a build up of pressure. You need a vent pipe, stack or stench pipe somewhere.

 

[studor]

Sounds like you need a 2 way vent you can tee a Maxi-Filtra on to the soil pipe check out HummBusters on the internet.

 

[studor]

Just seen where you are located. Contact Studor Australia

 

[Allan74]

Just wondering how you went with your septic tank.

We have been having dramas with our tank and a neighbour gave us eco tabs which has worked wonders. Smell was gone in 5 hours and never came back. One tablet per month and they aren't expensive.

Good luck.

 

[bambibasher]

If the septic tank is smelling then stop using any antibacterial products down the toilet as these kill the bacteria in the tank that eats away at the solids. If the bacteria has been killed off this will cause smells.