A question: why does my 1930's house have 2 outlets from the sewage inspection chanber

[NigelCollins]

NigelCollins, I'm curious about your drainage arrangements.

So no neighbour's drainage - why did you expect to find it running through your manhole?
Where is the kitchen waste ("the feed from the kitchen") outlet in the manhole?
What is the "top left vent" venting?
Does the"ensuite" have a WC?
If the bottom hole has a "load of gravel" in it how come its able to take (apparently) the total house drainage when its blocking the progress of your rod?

To answer your questions:
I assumed that the cover was over the main sewer that would run across the back of the house joining up the neighbors - I now realise that the main sewer is further down the garden (I know its there as I have seen house plans from 1930 - just couldn't work out how far from the house)

The feed from the kitchen joins the main toilet and downstairs WC before the manhole and all enter the manhole from the bottom of the picture.

The 'top left vent' is just venting the manhole. I have no idea why but it looks as if it was installed when the manhole was installed - about 80 years ago

Yes the en-suite does have a WC - has been there about 5 years

I assume (as someone previously mentioned that the gravel is at the bottom of a 'u bend' - the 'u-bend' was why I wasn't able to get a rod through and why (according to other posters) the top hole exists. I will use a wet & dry vacuum to clear out the gravel

 

[NigelCollins]

He also has rats!

Andy

When I looked at the 'droppings' they looked more like dead woodlice - so I'm hoping they are not rat droppings - we haven't had any sign of rats since living here for 7 years.

 

[endecotp]

Agreed. Does anyone have a diagram of what it's supposed to look like? I'm sure I've seen a good one linked previously.

http://www.pavingexpert.com/drain05.htm#exmh

That's it!

(It's hard to tell from the photo how far above the invert the branch is, but it's clear from the tissue that it is too high.)

 

[NigelCollins]

Agreed. Does anyone have a diagram of what it's supposed to look like? I'm sure I've seen a good one linked previously.

http://www.pavingexpert.com/drain05.htm#exmh

That's it!

(It's hard to tell from the photo how far above the invert the branch is, but it's clear from the tissue that it is too high.)

Is there anything I can do to improve the flow from the branch so that it does drop straight into the channel?

 

[HERTS P&D]

You can use a 90 degree joint fitted on the end on the pipe work so that the water flows directly into the drain channel, you might have to cut the pipe work back a bit.

Also they are rat droppings.


Andy

 

[NigelCollins]

You can use a 90 degree joint fitted on the end on the pipe work so that the water flows directly into the drain channel, you might have to cut the pipe work back a bit.

Also they are rat droppings.


Andy

Thanks for that - I'll see what screwfix have and sort it out.

Is there anything I need to do re the rats dropping - obviously I have no idea how long they have been there so don't know if it's a current problem

 

[vinn]

NigelCollins,
Thank you for the detailed reply.

There should be another manhole at the point where your house sewer joins the common sewer at the bottom of your garden - although I wonder if your plans were actually showing a main sewer running in a road?
Where your kitchen waste joins the soil pipe drain there should be an inspection chamber or a manhole.
Buy a correct diameter expanding rubber drain plug from your local plumbing suppliers, & plug the top hole (trap clean-out).
Eliminate the manhole vent - dig it out or pack with semi-dry sand & cement. Its not necessary.
Surprisingly, the ensuite discharge stub has worked for some years without blocking the benching or channel but it would do no harm to do as others suggest.
Given that the trap has "worked" all these years then leave it alone - although its typical to eliminate them.

Regs require that all drainage connections and sharp bends need an inspection chamber or a manhole (in case of blockages) but if it works without an access here & there then leave well alone.
Pack all the gaps in the manhole walls, & around pipes, with semi-dry sand and cement - rats can get into the soil and burrow up into the garden,

 

[vinn]

newboy,

I'm afraid that you are wrong on both counts:
I already knew what it was, and had earlier named it as a "house trap" - perhaps you were confused, and mistook my questions about the manhole for queries about the "house trap"?
AAMOI, both prince of darkness and stuart45 (diagram posted) had described it earlier in the day so the OP was, by the time of your post, well aware of what he had.

 

[stuart45]

The 'top left vent' is just venting the manhole. I have no idea why but it looks as if it was installed when the manhole was installed - about 80 years ago

It's not so much a vent, but an air intake valve. They were put on the last manhole before the main sewer if an interceptor trap was used. The idea was to balance the air pressure and stop the trap from emptying of water. There should be a mica flap outside to stop any sewer gas from escaping. Most of these don't work anymore and it may have been broken off and buried anyway.

 

[NigelCollins]

NigelCollins,
Thank you for the detailed reply.

There should be another manhole at the point where your house sewer joins the common sewer at the bottom of your garden - although I wonder if your plans were actually showing a main sewer running in a road?
Where your kitchen waste joins the soil pipe drain there should be an inspection chamber or a manhole.
Buy a correct diameter expanding rubber drain plug from your local plumbing suppliers, & plug the top hole (trap clean-out).
Eliminate the manhole vent - dig it out or pack with semi-dry sand & cement. Its not necessary.
Surprisingly, the ensuite discharge stub has worked for some years without blocking the benching or channel but it would do no harm to do as others suggest.
Given that the trap has "worked" all these years then leave it alone - although its typical to eliminate them.

Regs require that all drainage connections and sharp bends need an inspection chamber or a manhole (in case of blockages) but if it works without an access here & there then leave well alone.
Pack all the gaps in the manhole walls, & around pipes, with semi-dry sand and cement - rats can get into the soil and burrow up into the garden,

Vinn - that's great information - thanks

The main sewer is definitely shown in the garden - see below

There is an inspection chamber - unfortunately previous occupants have placed a fence directly above it - not impossible to get to but very inconvenient.

I'll make the other changes you suggest.

 

[Newboy]

It's not so much a vent, but an air intake valve. They were put on the last manhole before the main sewer if an interceptor trap was used. The idea was to balance the air pressure and stop the trap from emptying of water. There should be a mica flap outside to stop any sewer gas from escaping. Most of these don't work anymore and it may have been broken off and buried anyway.

Usually look something like this

 

[NigelCollins]

It's not so much a vent, but an air intake valve. They were put on the last manhole before the main sewer if an interceptor trap was used. The idea was to balance the air pressure and stop the trap from emptying of water. There should be a mica flap outside to stop any sewer gas from escaping. Most of these don't work anymore and it may have been broken off and buried anyway.

Usually look something like this

yep - that's exactly what it looks like

 

[Hugh Jaleak]

The actual purpose of the vent on that chamber was to ventilate the house sewers. The Victorians had a bid thing about 'drain air' believing initially, it was the cause of most ills of that era, and then when drainage developed into the typical systems we still see today, they used an interceptor to seal off the house drains from the main sewer in the road. The idea then was, as air passed over the top of the stack, it would draw air into the system through the low level vent and then out through the stack, thus venting the system. The main sewers were vented independently with cast iron stacks in the street.

I would advise you do not fit a bung in that rodding eye. They can become dislodged in the event of surcharging in the main sewer, and then cause further problems downstream. Provided the bottom outlet is kept clear, and the flow can pass through here as designed, then the arrangement can be left as is. The rodding eye on the top was purposely provided to allow access through to the drain/sewer beyond the interceptor to allow rodding access in the event of problems, and therefore a blind connection to the sewer was often the case.

Where is Newboy 'wrong'? As far as I can see he has named the part in question as an 'interceptor', common name for it, and a common installation of that era, right up to the 1940's, and his other points seem valid to me!

 

[vinn]

Hugh Jaleak,
Not only was newboy wrong on both counts but so are you on three counts.

Read the posts in question, and the sequence of date/times reference the house trap/interceptor business - they show that his attempt at correcting me & the OP was wrong.
It wasn't a case of identifying the trap by naming it, it was that it had already been identified by three previous posters.

I have no idea what you mean by "his other points" - he wrote nothing else that concerns me?

No one is disputing what the clean out hole is for, so why are you setting up a straw dog?
Why you have to describe the backing up of a house sewer line as a "surcharge" is puzzling?
What the OP describes as a "main sewer" is a branch sewer taking drainage from two houses, as far as we know, before it connects down stream at a main sewer.
The cleaned out hub would take a simple expansion plug with ease & permanency as probably millions of permanent in-situ stoppers demonstrate. It would also stop rats.
The notion that back up pressure would force out an expansion plug is therefore also wrong.

 

[stuart45]

https://books.google.co.uk/books?id...e&q=purpose of a mica vent on a drain&f=false

This article explains the idea of venting the system with an interceptor to avoid the loss of the trap water.