Durgo valve (air admittance valve)

[John Carlyle-Clarke]

We have a septic tank in the garden and an underground soilpipe that feeds into it. The downstairs toilet drops into it via 110mm plastic pipe, which has a vent up through the roof. The downstairs bath and sink use standard 2" waste which feed into an open ground level drain outside.

We added later an upstairs shower room with toilet and sink, which has a smaller (2" maybe) air admittance valve in a cupboard behind it.

We are now redoing the downstairs bathroom and want to remove the vent and replace it with an air valve inside the WC wall unit.

(1) Is it OK not to have an outside vent in the system? (2) How low can the valve be in the WC unit? I saw something about it being higher than the highest trap in sinks etc, but I assume this refers to items on the same pipe segment.

Any advice much appreciated!

[The Natural Philosopher]

No.

Durgos work as anti=siphoning systems. But a positive pressure relief system is also needed. There must be at least one open vent somewhere.

However you can simply run a pipe into the loft space and take it where you want..if the loft is cold..I THINK its OK just to exhaust there. Or run a pipe to a gable.

DO be careful though..horizontal pipes with sags in them collect condensation in cold weather, and thus dribbles down th vent out flow.. best is to either have an uphill run to the exit, so water runs down to th drain, or an 'arch' so that at let the water run out as fast as its condensed, and doesn't collect. DAMHIKT.

[John Carlyle-Clarke]

It's a chalet bungalow so no loft to speak of.

Would the open drain outside into which the kitchen sink, and downstairs bathroom bath and basin feed, not act as a positive pressure vent? I don't know if it has an integral trap or not.

There are also two open rainwater drains where rainwater downpipes feed into the soil pipe (not allowed on new build, I know) although I believe these have traps in them.

The septic tank itself has vents also (round open 4" clay pipe recessed into the ground which leads down into it).

[The Natural Philosopher]

It must have a trap by law, so no, it wouldn't.

IF you are flooding a septic tank with rainwater, you have a problem. Thy cant be expected to not dump fairly raw sewage out of the outflow when it rains..

Fine, if the soil pipes aren't blocked..this is an issue..positive build up of explosive methane. As well as whiffs at ground level.

The whole point is to NOT have concentrated bubbles of methane and smells bubbling up from traps and ground level vents, where flames may be reasonably expected to ignite them.

Methane is slightly lighter than air at normal temps and pressures, therefore high level venting 'sucks' the methane out of the drains and disperses it reasonably harmlessly above habitable levels.

In this context your septic tank vents are actually more air INTAKES than exhausts..

Look nothing says you HAVE to do things by the book especially if the BCO is not involved, but its worth understanding the rationale behind the regulations, so you can make an informed decision.

I am not a fan of over regulation. But most of the regs are sane sensible cheap ways to avoid unecessary risks.

[John Carlyle-Clarke]

I agree, it doesn't seem like a good idea but this is how it was built in the mid '60s and I was told it was a common practice until the regs stopped it.

I see what you mean. I did search the net a lot and there does seem to be confusion around on this. I got the impression that the need for a vent was acute when you had a sealed drainage system connected to a public sewer. The system I have seems so not air-tight that removing the vent seemed reasonable.

Agreed, I'd like to take a pragmatic approach but I don't want to take unnecessary risks. I know where I can dig and access a plastic 4" section of the soil pipe underground (I filled the hole in when the extension builders left it). Presumably I can tap into it and run a small (say 2") pipe up the outside wall of the house and up to a little above roof level? That way I don't have to punch through any exteriors walls or roof.

That would place the vent about mid-way between the two toilets on the main 4" pipe. Is that a suitable position? Would 2" pipe be big enough for a vent?

By the way, do you have any idea about the height of the durgo valve? :) For mail, replace null with net.

[Doctor Drivel]

When on a septic you need an open vent on the main stack that draws air in and out and releases methane gas. On some legs off durgos can be fitted. Look into HepVo traps, by Hepworth, which are air admittance valves.

[Adrian]

The gentleman who built this house cunningly extended the top of the soil pipe into the gap between the roof tiles and the plasterboarded ceiling in the upstairs bathroom..

Not a good - plan - nasty smells in the house when the wind's in a certain direction.

More out of hope than anything else, I added a 'durgo'-type valve on the open end of the stack - but (of course!) it's fine at allowing air _into_ the stack when the toilet flushes or the bath empties, but we still get pressure biuld-up & foul air coming back up from the septic tank and passing round the various water traps - so nasty smells again...

Yesterday I purchased the necessary bits to connect a 2" pipe into the top of the existing stack, and run outside the house and up the gable end - thus (hopefully) allowing the noxious fumes to find their way out of the system and away... (Because of the way the 4" pipe has been taken into the house through the soffits you can't just extend the stack up in

4").

If it wasn't snowing at the moment I'd be out there fitting it all together... perhaps tomorrow....

Doncha just wish people'd do things right the first time !?

Adrian

[The Natural Philosopher]

I believe that is in fact a completely to-the regs way of doing this. I have seen victorian cast iron 'smokestacks' with decorated tops protruding out of sewers before now ;-)

Position is fine..its genrally 3" or bigger pipe though, but I don't know what t rgs actually say..

Higher than the highest fault water-level of the sink, basin, bath or toilet cistern, for obvious reasons..

[John Carlyle-Clarke]

Sorry to be dense, could you explain a bit more?

[John Carlyle-Clarke]

To (hopefully) clarify matters, here is an approximate diagram of the existing system.

've marked where we're proposing to remove the existing exterior vent, and where if required I'm thinking we could tap the external underground soil pipe and add an vent pipe to roof level up the outside wall.

I've omitted the rainwater drains for clarity/laziness.

[Rob G]

John You don't say whereabouts you are which is probably just as well given that the rain water into your septic tank will be flushing raw sewage (as said previously) into, in all likelihoods (1960's building), the local water course. I would seriously consider getting that resolved before the LA or other environmental organisation catch up with you and hammer you for the pollution.

I should point out that your jibe about 1960 regs. certainly doesn't hold in central Scotland where many septic tanks in rural districts were installed in the 1920's and AFAIK rainwater into them was not allowed then. I would suspect you're suffering from a cheapskate build rather than a regulations weakness.

Rob

[Doctor Drivel]

[John Carlyle-Clarke]

Thinking about it, I'm only going by the say-so of one builder, who wasn't actually much good. Two rainwater drains *are* along the line of the soilpipe, but I don't know if they go into it or into soakaways. The other downpipes on the building do go to proper soakaways.

He suggested putting a new rainwater downpipe (created by the extension he built 6 years ago) into the soil pipe after the BCO had signed off. I didn't take his advice on that!

It's quite possible that he was wrong about the other two, as the original build does seem to have been of generally good quality. Perhaps I need to get an assistant to pour a bucket of water into one while I watch under the inspection hatch on the tank and see if it does flow in.

[The Natural Philosopher]

So the durgo dosn't become the default point of overflow.