On 3 Mar, 22:50, John Carlyle-Clarke wrote:
John Carlyle-Clarke wrote:
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!

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

http://www.carlyleclarke.plus.com/Drainage.png

I'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.

--

For mail, replace null with net.

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