Drain / Sewer question

[dal5band]

We've been looking at a 30's house my son is buying and the surveyer said the drains were blocked. We looked for ourselves and discovered that although the drains are not blocked, there is static water in the half pipe in the manhole, about 2 inches deep. When you flush the loo, water does go out of the outlet side and you can hear it splashing down into a sewer. It seems that the outlet pipe lip is slightly higher than the bottom of the half pipe - it almost seems it was installed this way. There is no cracking in the cement or clay pipes.

Is this some kind of inteneded design ?
or has the manhole and house side just sunk by a couple of inches ?

The manhole, soil down pipe and kithen drains are all within 3 meters - what would it cost to relay the whole lot ?

 

[^woody^]

It may have been laid like this, but it seems that part of the run has dropped, causing a backfall, or there could be a blockage. Either way, there should be no standing water.

You need to have the drain camera surveyed to determine the extent of the problem, and then the company can a cost estimate from this.

It may be possible to relign it, rather than re=lay the drain, but it depends on the cause

 

[dal5band]

Thanks

 

[noseall]

i have come across this scenareo recently. on the outlet side of the inspection chamber the builders had installed a trap like system whereby the fluids flowed freely below but the solids struggled.

weird i know.

i have also encountered traps along main underground runs!

the only thing i can think of is it may benefit a septic tank type sewer system.........maybe.

 

[dal5band]

we've had another opinion from a surveyer who happened to be doing another job - he agreed that it looks as though it was built like that but not necesarrily by design - probably a Friday afternoon job! As the kitchen and rain drains also go into this chambre there is plenty of flow to keep things moving.

 

[Nige F]

sounds like an interceptor trap.......they usually end up blocked and running out through the long-gone rodding eye above the channel.....In fact we only used to replace the rodding eye cover if we wanted to get more work unblocking it again in a month or 2

 

[dal5band]

That's exactly it ! There is a clay pipe about 12 inches above the outlet pipe which looks like a handy overflow but is in fact the rodding access to the sewer downstream that Nige F mentioned.

 

[dal5band]

Had a Thames water man look at this manhole :

Discovered how this intercept trap works - the outlet is at the bottom of the channel and hidden when it's blocked. It goes down and then persumably comes up (U bend) into the sewer. Because it is silted up you don't realise it's there.

What I thought was the outlet is in fact the rodding access, 3 inches above the channel but working as an overflow outlet.
The pipe 12 inches higher up is a vent - there was probably a stand pipe vent somewhere nearby in the past.

 

[Nige F]

close there are tall vent pipes in the street, but not connected to your manhole .......there would`ve been a metal box thing like a knight`s helm..in your garden with a mica flap behind a grating to let air IN to your domestic drain ...the interceptor was to disconnect airflow from the main sewer....like me and my skills all redundant and old hat nowadays .............pass the luger ....silt posh shyte in Surrey then

 

[dal5band]

No, not the brown stuff. The trap is full of sand / silt - I think it gets in via the open kitchen drain.

 

[Nige F]

just testing