Soil pipe joint leaking at first floor, is it blocked?

20 Jul 2007
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United Kingdom
Our soil pipe stack is leaking from a pipe joint where it enters the flat roof of our extension. I noticed a tiny pool of water on the dry roof when looking out the window today.
Photos show pipe joint and leak.
Upstairs taps, bath, sink and shower all drain properly but upstairs loo often needs several flushes to clear.
Downstairs sink occasionally drains slowly. Sink sometimes smells bad when the Dishwasher and Washing machine drain into it's U bend.
Soil pipe runs horizontally through our extension roof before dropping vertically at the rear of the house. Soil pipe vent stack dosent have a debris cover. Occasionally when it's raining outside water trickles down an internal wall for a short time. There are no bad odours in the house.
Is the soil pipe partially blocked?
Last edited:
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Rare for vertical sections to block, but not impossible. First port of call would be to check the underground drains are clear, if you've a blockage underground it plays funny tricks with appliances upstream.

Are there connections into the stack above the point in your photo? Stack may not be blocked, but discharge from a bathroom could be enough to cause a slight leak. Pipework look like its a few years old, the UV in sunlight attacks plastics over time and sends it brittle, possible there a slight crack or the seal in the joint isn't as tight as it once was, just enough to allow a slight weep past.
thanks for replying.
The trickle of water is visible again today buy it's from the rubber collar where the flat roof membrane meets the soil pipe vent and not the actual pipe joint as I said earlier.

There are no inlets higher than the weeping rubber collar although the toilet joins to its left. (See photo, loo inside below window, leaking collar on soil pipe to its right.) Bathroom is behind the wall that shower pipe is attached to so shower, sink etc drain into soil pipe below joint. No other pipework on outer walls.
Drainage continues through extension flat roof then down outside.
Shower has been running this morning. Could it still be a partial blocked drain or a build up of water inside the boxed up section due to a cracked pipe? Or both?
This fitting looks in poor condition. To me it looks like it leaks on the back and flows round to the front on the rubber


Just saw there is nothing above. I bet it’s dew.
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Why not trace the manhole that goes to, lift the cover and then flush the toilet?

The toilet flush water should appear immediately flowing through the manhole, if it doesn't, there is a blockage or obstruction.
Does the WC flush ok? Classic signs of a problem would be the level rising right up in the pan when flushed, before slowly dropping again. As there's no connections above the junction, I'm with Ian, probably just a bit of dew.

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