UKC

Hoping there is a kind engineer or other knowledgeable UKCer able to offer an opinion.

We have a soil/waste plastic drainage system which involves plastic inspection chambers shared between several properties. There have been several blockages recently which appear to be due to one long, vertical soil stack delivering toilet muck into the chamber and "throwing" it into an unused and capped inlet opposite which eventually fills and then blocks the central exit channel from the chamber. This is based on a professional check of the system (including CCTV along the pipes) and we have been quoted about £4500 to have two inspection chambers replaced and the vertical stack altered, so it is no longer into a side inlet, but directly enters the central channel in the bottom of an inspection chamber.
However the properties were built in 1985 and have had no problems until recently so we feel it may be unnecessary to radically modify the system

Might a much cheaper solution be to fill the capped inlet completely (resin or concrete?) though this might simply lead to more rapid blocking if muck simply blocks the central channel earlier (at present it takes some time before there is enough buildup to start a blockage)? Perhaps we could experiment with some form of temporary block to the capped inlet.
Would it also be possible to consider slowing down the muck by introducing a roddable "kink" in the vertical soil stack near ground level, which at least should be easily reversible?

Is the price high so due to the use of scaffolding?  Maybe get a few more quotes.  

Putting a kink in is an interesting idea, it might need regular cleaning, which isn't a pleasant job.  

Has anything else changed since the properties were built?  

This is key.
Is it your stack in question?
Have you or others started using a low water volume bog, not enough fluid to flush the drains clear properly?

Thanks. The main cost would presumably be the underground work replacing two quite deep inspection chambers. I imagine only a little straightforward scaffolding or even just a tower would be necessary.

Yes, another quote (and reinvestigation) would definitely be a good idea if we considered going ahead. 

One change is that all the properties have probably had dual volume flushing replacement toilets over the years. The volume of water in the cisterns is almost certainly less and so there might be less washing effect of each flush especially when the lower volume flush is used. In addition one property had had a blocked toilet which had been unused for some time (CCTV shows its pipe to be clear now). Our old toilet was replaced after most of the blockage incidents (due to the drain engineer pushing the cleaning jet hose up the wrong pipe and smashing the bowl).  

Yes, our stack is the one in question. It is a vertical pipe from our toilet (joined by waste from our bathroom sink and shower/bath) and  joined just above ground level by an almost horizontal soil pipe from our downstairs neighbour. I've mentioned the new toilet situation in my earlier reply which probably overlapped with your post....hope this was sufficiently detailed. Our toilet does throw muck into the capped inlet BUT most of the blockages occurred before our toilet was replaced with a lower volume one.

Incidentally any costs for external waste/drainage are shared between the properties so I'm not posting to try to avoid any responsibility (and wouldn't anyway)! 

I think most of your DIY suggestions would be worth trying

If you look at soil pipes on tall buildings you'll notice intentional kinks using pairs of 135 degree bends to slow things down. 

Underground there is also a one piece large radius settling bend so that high speed  wasted doesn't damage the pipes.

You could also try to fit a deflector to the outlet in the manhole.

Thanks. Is the deflector a standard item and do you mean blocking the capped inlet (ie opposite where the muck enters) with something to fill it, and do you have a recommendation, please?

I assume the shares I inspection chamber connects to public sewers, rather than a septic tank.

If so it's the water companies problem to solve.

Message me and I'll send you my number if you want a chat. Or weak to Environmental  Health.....they have the power to get it put right

Unfortunately the inspection chambers were put in during building in 1985 and are some distance from the public sewer connection.

I'll wait and see first if there are any other suggestions and will probably contact you. Thanks for the offer.

Might still be worth talking to your local water authority. They had to adopt a load of private sewers and pumping stations a couple of years ago. You might get lucky. 

It's definitely worth checking with your water supply company first. I had a subsidence problem with my house caused by leaking drains. Once it was confirmed that the drain served both my house and my neighbors house it was classed as a public sewer and all the drain repairs were done, with no charge, by the local water company, even though the damage was entirely on my property.  

There was a change in legislation in 2010 ....Any private sewers or lateral drains that were build prior to October 2010 defaulted to the sewerage undertaker.

In other words they are no longer private but public sewers.

Speak to the water company first as the chamber and most of the pipe work is theirs.

If the faulty connection is a pipe that only serves one property....

a) if it outside the boundary of their land it's water company

B) if it is within the boundary of the property it serves i.e. the chamber and pipe are in the garden of house with dodgy connection......it is private. But environmental health can make the owners fix under Building Act 1990 section 59

Thanks, and to Dax H and flatlandrich76. It will definitely be worth checking with the water authority.

The situation might not be absolutely clear cut as the properties are a block of flats and each each being Shared Freehold ie they may be viewed as one property but it is certainly worth checking.

re deflector- you can get flap valves that plug on end of the pipe (to prevent backflow) that would control the matter coming down?

talking of which, a mate intends using flap valves to prevent sewage backflow in a combined drainage system. what happens when backflow closes the flap during heavy rain? presumably the water in the building rainwater/soil pipes back up until the hydraulic head exceeds the backflow head- potentially causing internal flooding?

Have you changed what you're flushing, sturdier bog roll, wet wipes, teenagers flushing anything nasty?

A wooden bung would be enough to test the theory about the spare port assuming you have sufficient access to measure and fit it. Make sure it can't escape and block the outlet!

jk

I've looked at an explanation of the regulations and unfortunately for a block of flats the drains within the curtilage (meaning commonly owned area I think) of the block are not the responsibility of the water company, even if they involve manholes and change of direction. I'll still check with the company anyway. 

In that case - speak to environmental Health - if it is just one connection that is causing the issues they can require the owner(s) of the flat(s) that use that connection to put it right - rather than everyone / someone not using the faulty connection

Thanks. I've looked at some on internet now. The underground plastic inspection chamber has a central gutter at the bottom (the entrance end of which takes stuff from another soil pipe and everything exits at the other end). Feeding into this are 2 inlets on each side: the pair away from the building being capped while  the other pair serve soil stacks.  The gently sloping inlets change from a tube to a gutter as they enter the chamber and empty into the central gutter. Some of the push fit flap valves would fit but because the fitting diameter is narrower than the soil pipe itself muck would probably accumulate and cause a blockage.

Regarding your mates problem perhaps the system will have the flap in a position so it is opened by rainwater pressure and closes when there is no rain?

Nothing changed apart from the toilet itself (but the first blockages occured before that). When the drain company surveyed we flushed single pieces of toilet paper and saw them "thrown" across the chamber and stop in and around the opposite capped inlet/gutter, poo without paper does the same. Over time this accumulates....at present I poke it into the central gutter and break it up every few weeks to keep things flowing.

A simple bung would only block the capped inlet where it was a tube but not stop accumulation in and around the gutter part of the inlet (as in my previous reply to EdS). The inlet gutter would need to have something filling it, but not raised, to minimize accumulations......but in fact, sudden thought....something large, and high n the accumulating corner of the chamber might work (but I don't know what).

We had virtually the same problem. Our down pipe from upstairs loo fed into main pipe at a junction beneath an inspection cover. The junction was essentially a 'crossroads', main channel running through from downstairs loo, joined by downpipe from the upstairs loo, with an unused channel opposite this. The capped, unused channel was just a few inches long.

Using downstairs loo was fine as waste ran straight through. When using upstairs loo waste seemed to fly across the main drain and build up in unused channel until eventually the main channel blocked. 

This was solved almost 20 years ago with no repeat of the problem. I cut an almost circular piece of wood (about 2cm thick) that lays flat above the main channel, on the underside of this I attached a small curved piece that fitted into the unused channel and blocks it off completely. Waste now comes down the downpipe, and hits the vertical piece that blocks off the unused channel and disappears as it should.

As I said, this fix has lasted almost 20 years. I'm thinking of re-doing it when I have time, although it still works fine, it's just I'd rather re-do it before the wood rots and it blocks again. It wasn't pleasant un-blocking it!!!

Thanks. Very useful. That sounds as if it would work. We'd probably need to block off a larger area than just the capped channel as sometimes the thrown muck appears to come to rest to either side.

Its odd that our drainage system has worked OK for 30+ years and probably other factors pointed out in previous replies might contribute. Low volume cisterns are now probably on all toilets emptying into the manhole; the chamber surface is probably much rougher due to limescale, grime etc; showering probably has less cleaning effect than the sudden egress of water  from a bath; the occupancy of the flats has increased with some people possibly using wet wipes etc (not down the long vertical pipe however).