1) Moving toilet 2) Shared soil pipes

How does water from the bath, kitchen and washing machine get to the soil pipe? And will it have to go further?

sounds like from the point the pipe crosses your boundary to the neighbour, the pipe becomes the responsibility of the water co (STW?)

Have they considered a "durgo valve"?

I don't see why as

I think so, see highlighted section ...

Photos including the existing toilet inside, immediately outside, and further back showing the general layout of the inspection positions and the shared soil pipe are at

I agree it looks as though it will probably work ok as it is so near the inspection chamber, but you may have to find another builder if the existing one interprets the regulations as saying he has to provide an air vent.

Saniflos are noisy and occasionally cause problems, but they are a lot cheaper than digging a new drain.

They are a last resort and must not have anything beyond s*it, piss and toilet paper down them. Sanitary towels and tooth brushes are an absolute no-no. Even hard lumps of s*it are not always digested

As long as you have fall, *do not use them*

Sewage pipery needs to be around 4" dia with a >1:100 fall from the pan u-bend. Basins and baths need similar fall but 2" pipe is OK.

Building regs don't care where it all goes with the sole proviso that every inch of it must be rod-able

Sewage systems need to be vented either with a high 'exhaust pipe' or at least a one way valve to stop U-bends being sucked dry.

That is all you really need to know, and stick to those regulations: They are well founded

If you want chapter and verse about needing your own soil pipe. contact building control: They are usually incredibly helpful and are mostly free and have authority over builders.

BUT having said that, if it's mini digger time and cut a new course, it doesn't take a lot to do a few extra yards.

And if you do get blockages, it makes things easier than having to knock up next door and lift their inspection covers.

There must be one already. Its mandatory on all sewage systems. What isn't mandatory is one per toilet etc etc

The implication of the OP was that there was only one on alternate houses. I doubt if that would meet regulations even if it worked. It would probably work ok if there is only 2.5 of not very steep pipe to the inspection chamber, but as you say I doubt it would meet regulations.

It would and it might well.

Essentially the purpose of the vent is to allow methane to escape from the whole sewage system. So it prevents any positive pressure build up

A secondary purpose of not allowing a vacuum either, to avoid sucking U bends and traps dry, is cated for by additional Durgos type valves where requeired

I think it would.

But in such matters talk to the BCO at your local council BEFORE starting work. They like that.

I cannot see why a trench needs digging, your bath and basin wastes seem to empty in a gully and you can bet your bottom dollar that under that gully will be a 4” clay pipe. Did your plumber lift the manhole cover? I would expect there to be at least one pipe entering it if the toilet and other wastes are combined underground or more likely two, one for the toilet and one for the bath/basin waste.

If you have as outlined above and are concerned about venting, you can attach a soil stack to the wall and feed it into that existing for the basin and bath underground waste pipe. The stack may need cranking at the bottom to avoid the window but both toilet and bath/basin wastes can simply be fed into the vertical stack.

That’s the system here, every second house has a vent pipe, alternating with those that have internal Durgo valves.

Good point. The builder has not as yet lifted the manhole cover. It has dropped an inch or so on one side and he is planning to rebuild it as necessary.

I'm not concerned about venting. It has worked as is since 1968 and I don't want an unnecessary soil pipe. The builder has thus far said I must have one. I'm trying to ensure I have evidence that shows that the current arrangement is satisfactory.

There is. That's how this thread started. It is clearly shown on the photo on my neighbour's bungalow.

I am trying to establish that, contrary to the builder's view, there need be no change to that arrangement just because a minor change in alignment of the outlets on my side is taking place.

Is "here" bungalows as well? Do you know the regs that allow that? How does one establish whether and where Durgo valves are?

Ask a BCO. Seriously. Costs nothing bar a cuppa and some bikkies

If builders were that smart they'd be politicians

This is a 'sewer wide' issue. It does not require one stack per house. many stacks were built as street furniture.

So you may need to install a Durgo where a toilet connects to a shower or bath trap directly. Durgos are on a per bathroom basis often as not, if all the appliances share the same pipe into the manhole

I have two routes out of my (private) sewage system, that join under a manhole. Each serves two bogs, two showers and one or two baths.

One has an eaves level vent. the other has just a Durgo.

With hindsight I would probably have put in two vents, because Durgos are not 100% perfect and can allow a little suck.

But its good enough

Yes, that seems a logical route. I hope that they can attend without undue delay as the project has been brought forward to week after next.

I'm not doubting the need for vent stacks.

ok, so that I understand and as per photos we have spoil water and bathroom waste going via separate pipes into the same inspection chamber so there must already be something installed eg a Durgo valve.

And if the plan is to use the same pipe for spoil (eg toilet) water and bathroom water then a Durgo valve is definitely required.