The Natural Philosopher wrote:
John Carlyle-Clarke wrote:

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.


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..

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.

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..


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.

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.

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.