Leak in carpark from flat

MyRealNameToo

So, we live in a building constructed around 2005, to me it's a slightly odd setup with three layers of properties over 5 floors of building.

• Ground floor - has a small foot print of building which houses the ground floor bedrooms of the maisonette's and the main entrance, the rest of the building is supported on pillars with the space under it being used for car parking
• First floor - the main space of the maisonettes and the stairwell for the rest of the building
• 2nd floor - 1 bed flats
• 3rd & 4th floor - 2 bed duplexes but similar to ground the 4th floor is only partial and they have a roof terrace on the rest

The Maisonettes and Duplexes go all the way from front to back of the building, the 2nd floor flats are on either side of a corridor.

Underneath the party wall between us and one neighbour, in the carpark there are 3 soil stacks emerging near the middle of the building then one more further along. The one on our side is the soil stack for our ensuite, the one one further along is our kitchen though the separate WC goes in there too. The other two are a mystery allegedly.

There is another soil stack on our side of the party wall to the other neighbour/side which isnt ours. As you walk the party lines the pattern of the ensuite soilstacks are consistent but the ones on the other side range from 0 to 2.

So, there is a leak that is coming out around the soil stack to our ensuite See diagram below, we are flat 3 in the ceiling plan and the yellow stack is leaking. It's about 2-3 drops of water a second but is basically constant. Started 2 weeks ago and was much less, has gotten worse. According to the "plumbers" the Freeholder has sent out it is a shared soil stack but they dont know what the other two are there for. They have put coloured dye into the water of each of our appliances in the ensuite and one of the neighbours above but the water runs clear from the dripping. They havent gained entry to the final property.

(E is ensuite soil, K is kitchen soil, U are the others that are visible but unexplained)

Have partially exposed the soil pipe in our ensuite (its all boxed/tiled in) can see the basin and toilet connections and it looks dry, the pipe itself has minor marks from dried water above our connections. The connection from the bathroom isnt visible and no signs of it in the separate WC in the adjacent room.

We have had a bit of a leak in the WC in the past from the cistern, most the time just when it's flushed. This has been isolated since but the isolator is allowing a tiny flow through so it was still dripping 1 drip a minute. This has now been resolved by removing the hose from the cistern and putting it into the sink.

Around the soil stack its modestly damp at ground level but no standing water. There was a single drop of water on the copper pipes going behind the soil stack.

So the freeholders plumbers idea is that it isnt a waste water but a supply water leak, maybe its the dripping cistern in the other room and the water has travelled along the pipe and fallen into the soil stack and come out there. The stop !!!!!! it turns out has also ceased so can't turn it off to see if it's a supply issue.

I'm struggling with it though… 1 drip a minute causing 2-3 drips a second elsewhere just doesnt add up to me. There is no sign of water escaping in our property but everything is fully tiled with no access ports etc. I still think it's likely a waste issue, the dripping got faster last time checked when the ensuite basin was running but they say no dye came out. Maybe it's slow to escape around the stack? The space between the floor and the pipe is full of horrible looking goop.

We dont have an individual water meter to see how its moving.

Any ideas?