New connection to deep manhole

[endecotp]

Dear Experts,

Today I've visited someone who is considering moving their downstairs toilet.

They have a concrete-surfaced back yard with a deep manhole, with a shared sewer at the bottom serving the row of houses. There are several pipes entering the manhole, two at the bottom with proper flaunching and angled correctly (including the existing loos) and a couple of other pipes just below ground level, one from a kitchen gulley and the other uncertain.

First question: this is certainly a shared sewer owned by the water company, but how much apart from the sewer pipe itself do they actually own? I.e. is permission needed to modify the manhole, to connect a new pipe? Or does the householder own the structure above the sewer pipe?

Second question: is it acceptable for a toilet connection to enter a manhole half way down and fall vertically?

If it's necessary to connect at the bottom, that would require digging a huge trench. Someone else has apparently suggested trying to join one of the existing pipes somewhere upstream of the manhole to avoid the need for all that digging, but that seems to have its own issues due to gradients.

Sorry no photos. Thanks.

 

[stevie888]

If it's a public sewer then you'll need Water Co's approval to join into the manhole.

A backdrop is the usual approach to joining a shallow run to a deep sewer.

 

[Hugh Jaleak]

All connections should really be at or just above Invert level and in direction of flow, but WC Connections are a must, otherwise solids will start collecting on the benching and before long, cause a blockage.

Secondly, if a Shared Sewer, the Water Co are responsible for the lot, the pipes, chamber and even the cover. Any connection will need their Permission and will have to be done to their specification. They are likely to insist on an external Backdrop, and may even demand the current high level inlets are diverted to connect into the new pipework so they discharge at the bottom of the chamber.

Where does the drain for the existing Ground Floor WC run, and is there any scope for diverting this to the proposed new WC position?

 

[noseall]

Dear Experts,

Today I've visited someone who is considering moving their downstairs toilet.

They have a concrete-surfaced back yard with a deep manhole, with a shared sewer at the bottom serving the row of houses. There are several pipes entering the manhole, two at the bottom with proper flaunching and angled correctly (including the existing loos) and a couple of other pipes just below ground level, one from a kitchen gulley and the other uncertain.

First question: this is certainly a shared sewer owned by the water company, but how much apart from the sewer pipe itself do they actually own? I.e. is permission needed to modify the manhole, to connect a new pipe? Or does the householder own the structure above the sewer pipe?

Second question: is it acceptable for a toilet connection to enter a manhole half way down and fall vertically?

If it's necessary to connect at the bottom, that would require digging a huge trench. Someone else has apparently suggested trying to join one of the existing pipes somewhere upstream of the manhole to avoid the need for all that digging, but that seems to have its own issues due to gradients.

Sorry no photos. Thanks.

Agree with Hugh, try and identify one of your own drain pipes leaving the house and connect to that.

 

[endecotp]

Thanks all, that's very useful. There is a slight slope over the yard and the new location is somewhat lower than the old one, so connecting to existing pipes is difficult because of gradients.

I've just googled "backdrop". Are "internal backdrops" often used? That might possibly be a solution involving least excavation.

 

[denso13]

I've just googled "backdrop". Are "internal backdrops" often used? That might possibly be a solution involving least excavation.

Not usually, but you'll also need LABC approval who will have their own say on things.

 

[stuart45]

Internal backdrops are sometimes used. When building on new work external is easier because it's already excavated. For retro internal might be used if there's enough room to work.

 

[endecotp]

Very rough sketch. House wall in black. Existing deep sewer runs right to left. Existing pipes from house in blue; proposed new pipe in red. Ground is slightly lower to the left.

Connecting to an existing pipe would require a sharp left turn (probably tighter than the diagram suggests). I don't know where the existing pipes drop, i.e. whether there is a backdrop at the manhole or whether they run at low level from the house. Joining to them low down would involve a deep excavation; joining at shallow level might require running up hill.

 

[HERTS P&D]

What is the depth of the manhole?

Andy

 

[endecotp]

What is the depth of the manhole?

Andy

I counted ten courses of brick, then the concrete benching. Hmm, that's not much more than a metre; it looked deeper than that.

 

[stuart45]

They always look deeper when you're looking down. That's probably around 12 courses, or 3ft.
What's the length of the run?

 

[endecotp]

What's the length of the run?

For the proposed red line, very roughly 5m maybe?

 

[stuart45]

So you need about a 5 or 6inch fall. Can you get the depth at the other end easily?

 

[endecotp]

So you need about a 5 or 6inch fall. Can you get the depth at the other end easily?

Getting the fall along the red line would not be a problem. The challenge is that that would require a lot of digging, and getting permission.

Getting the fall to connect to one of the existing drains would depend on how deep they are, which is unknown.