Fat Berg in the Communal Drain system.....

Nick_C

I would have carefully poured a bucket of two of caustic soda solution down the drain before calling anyone else out.

EachPenny

There are some good reasons why upper floor flats are worth more money.

As others have said, fat deposits normally build up where the temperature of hot fats reduces to a point where it starts to solidify. Usually that will either be a certain distance from the point the fat enters the drain, or else where it suddenly encounters standing water like at a blockage or an interceptor trap. Given that foul water waste is generally quite warm and rich with detergents and surfactants, it is normally unlikely you'll get excessive fat build up in shared vertical pipes.

What is interesting about this case is if the partial blockage was downstream of the ground floor connection, then before the first floor would have problems with water not draining from a sink you would expect the ground floor flat to have sewage bubbling out of their toilet and bath. In fact to stop that kind of thing happening, it was (still is?) common for ground floor drainage to have a separate connection to the sewer rather than being connected to the shared stack.

For both the ground and first floor flats to be affected, but for the ground floor not to be flooded, it would suggest there is something unusual about the pipework. The ground floor flat owner might want to find out if they have a non-return valve of some kind on their connection.

moneyistooshorttomention

AFF8879 wrote: »

For the sake of the first £150 I would just suck it up and take the hit, but I'd also make sure to drop a polite note through each flat's letterbox explaining the issue. You could also inform the council as if the issue is persistent its eventually going to cost them money. Most blocks have a notice board in communal areas so that's a good place to start.

You say your tenant has been there over 18 months and I assume this is the first instance of the problem- so at least, if it has been continuous, that timescale will be your minimum "loop" until you have to cough up again

If you decide to take that route - I'd keep evidence you'd done that - just in case of future need (ie if you needed to prove the culprit would reasonably be aware not to do it again).

moneyistooshorttomention

Nick_C wrote: »

I would have carefully poured a bucket of two of caustic soda solution down the drain before calling anyone else out.

I get the point - but isn't that not a very safe idea from the pov of the person doing it? (ie caustic soda being a bit :eek: I thought I'd remembered).

OP probably has the same philosophy a lot of us (me for instance:rotfl:) have of "If it looks like it's going to be at all :eek: - then pay a tradesperson to do it - as that is a part of their job they expect to encounter sometimes/have any necessary protective gear etc for".

Nick_C

I've used caustic soda several times. It's very effective. Follow the instructions. Be very careful. Avoid splashes. Consider using eye protection.

00ec25

moneyistooshorttomention wrote: »

I get the point - but isn't that not a very safe idea from the pov of the person doing it? (ie caustic soda being a bit :eek: I thought I'd remembered)..

there are several over the counter liquid unblockers that are very strong and very effective. Of course that does mean one has to be slightly intelligent to use them and know better than to pour them over your hands.

"One Shot" is a very good version that is about as strong an acid as you can buy without a licence (it's 91% sulphuric acid!) yet is readily available in DIY and hardware shops

this link is picked at random, I have no connection with the seller

https://www.selcobw.com/one-shot-drain-cleaner-1-ltrCleaner/dp/B01MRKM2GC/ref=pd_lpo_vtph_201_bs_lp_t_1?_encoding=UTF8&psc=1&refRID=98DCEHF4MC52P7G8GCPW

davidmcn

I believe the professionals advise against the chemicals on the basis that if it doesn't work they'll just end up having to deal with your fatberg (or whatever the blockage is) plus your caustic chemicals still trapped in the pipe.

Nick_C

Well the professionals will advise against it because they are losing the opportunity to make money from you.

Isn't a strong alkali more effective at dissolving organic material than acid?

And if it doesn't work, it can easily be neutralised.

Davesnave

I'm not convinced you'll get evidence sufficient to pin the blame on anyone. It might point in a particular direction, but proof is something else.

My practical experience is too long-winded to recount here, but recent extensive replacement work on our private drains has convinced me that build-ups of fat can hang about undiscovered/undislodged for years. If this is the case, then it's possible someone responsible for causing a blockage might be no longer resident when the problem occurs.

pinklady21

Thanks everyone for the replies - much appreciated.

The word from the drain jet company is that they first jetted through the kitchen sink drain, which resulted in a lot of fat coming through the overflow into the sink. Ick.

I also asked them to remove the drain cover outside and see if there was anything there. They said the drain was running, although slowly, but when they jetted towards the stack, a lot more fat and other debris including toilet paper appeared, which must also have been contributing to the blockage.
Impossible to know how long it has been like this.

Got me thinking about the location of the drain pipes inside and whether there are 2 stacks - 1 serving the toilets and another serving the sinks. That would explain why it is only the sinks that are being affected and the flats are not up to their ears in sewage from the ground up.

The drainage pipes in the flats have all been concealed behind a wall, so rather than do any intrusive investigations at this point, I will see if the Council (who originally built the block) have any plans showing the drainage route.

re suggestions about using drain cleaner - my tenant advises she has been using lots of Mr Muscle and a manual unblocker plunger type thing for ages to try and get the sink to drain. While it worked for a while, the drain eventually refused to work and the water just sat in the sink.

I have had historical problems with the kitchen sink being slow to drain, which suggests that Davesnave is right - this had been an ongoing problem that has gradually built up over the years.

Anyway - if I can get hold of some detailed drainage plans that may help. Thanks all!