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My daughter lives on the first floor of a house in London that has been converted into 3 flats. The people on the top floor have a toilet which drains to the outside of the building, then drops 6m down an external waste pipe to an elbow bend below the ground and discharges into an inspection chamber. The problem is that the effulent splashes up and sticks to the wall of the inspection chamber about 150mm above the channel. For 13 years since the house was converted into flats this has not been a problem. Indeed the problem may not have existed. But It is a coincidence, that since the arrival of a new occupant and his girl-friend in the flat upstairs, this debris, which is entirely toilet paper and associated debris, has built up until it blocks the inlet of this pipe. It does not appear to affect the inlet of other pipes, nor the outlet of the chamber. This implies that the debris buildup (slowly over the period of 3 months) spans at least 300mm across the invert channel and eventually reaches and blocks the mouth of the inlet pipe. This blockage causes a backup of effulent which eventually appears in the kitchen sink of my daughter's flat. This has happened twice in the past year. On both occasions a contractor was called and he cleared the blockage. His advice was that the whole inspection chamber should be dug up and replaced with a new inspection chamber incorporating a "gentler" bend for the foul water drain from the two flats. The cost of the work is estimated to be £3000.
I am thinking that the solution might be a short length of plastic guttering, cut to size, shaped to fit, and placed over the channel leading from the inlet to the invert channel. This could be cemented or a heavy weight placed ontop to keep it in place. I am hoping this solution will keep the debris from splashing up onto the far wall. You can see from the photo that the lower levels of the chamber are completely free. It is a bodge, but it could save a lot of money. Has anyone any other suggestions please?

The attached photo shows the inspection chamber 2 weeks after it was last cleared. The inlet from the toilet is at 7 o'clock and the outlet is at 3 o'clock. The chamber is located in a narrow alley between two buildings hence the cost of the work.Image
20201104_view of Inspection Chamber.jpg
Inspection Chamber 2 wks after cleaning
20201104_view of Inspection Chamber.jpg (199.01KiB)Viewed 5070 times
Hmm! so you want to fix it by botching a botch?

'his blockage causes a backup of effulent which eventually appears in the kitchen sink'

i would quickly call building inspectorate and thames water out in the morning, whoever conducted the renovation work is accountable.
Thank you REDSAW for your comments. The renovation work was done in 2007, so I do not think Building Control will be interested. Apparently, the lady in the bottom flat had in the past invited Thames Water to visit the site when she noticed effluent seeping out from under the inspection chamber cover. Thames Water said it was not their responsibility as the chamber is not outside the property boundary. In the meantime I am still hoping that someone will comment on the practicality of building a shield over the inlet opening to prevent the effluent splashing up onto the wall. I am worried that the "gentler bend" suggested by the contractors might not solve the problem because of the lack of space.
the kitchen sink should not be directly piped to the soil drain, there should be an air gap ie cut pipe over a gully trap.
it would be easier to fill a double rubble sack with polystyrene and shove that into the chamber.
Thank you REDSAW for your timely and helpful comments. I particularly liked your comment that the waste pipe from the kitchen should be discharged into a hopper mounted on the soil pipe. The air gap created will solve the problem of the water backing up into her sink. Your other suggestion concerning the rubble sack sounds very practical and should also do the trick. Thank you very much.
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