There are repeated problems caused by blockages in the external drainpipes used on most of Edinburgh's 100-year-old tenement buildings. Sometimes a block near ground level, sometimes a blocked vent pipe, sometimes siphoning of water from sink traps, cause unknown.
And, nowadays at least, it seems to be allowed that people can run sink drains into external WC drainpipes.
What's the best anti-siphoning design for a water trap? The basic S shape seems inadequate.
You could always try HepVo. We have three (bathroom & cloakroom). Seem to work OK.
An air admittance valve/fitting somewhere in the waste pipe, or, an anti-siphon U bend. These let air into the sytem, but dont allow it out, so, in theory, rather than sucking water through the U bend, it should allow air to be sucked in instead. Something like these:
Yup. No siphonage, no blow-back, no evaporation etc.
They're good in Northern tenements with outside pipes - no water traps to freeze.
Don't whoever cleared the blockage know what caused it? Likely the usual suspects - nappies etc. And fat.
I fitted one to a sink that takes a lot of crud from various breeds of take-aways and it's given no trouble for about 10 years now.
In article , Windmill writes
On the blockages themselves I have had experience of these on external stacks on Glasgow tenements which are generally 6" cast iron for soil and 3" cast iron for waste water.
I haven't seen problems on the soil stack but have seen it on the waste stack. Corrosion on the inside of the pipe gives a key for hair and washed off skin/body fat which eventually builds up on the pipe. Once this builds up to a certain thickness it appears to fall off in lumps leading to blockages.
Our solution is to periodically clean the stack down with a strong caustic soda solution. I make up half a kilo of caustic in a 2 gallon bucket, pour it down the bath trap, leave it for thirty minutes, half fill the bath with hot water then let this go at once to flush down the stack. The idea is to repeat this at each floor, starting at the bottom but of course this requires the cooperation of all owners/occupiers.
With this approach I've not had a problem with traps being sucked out.
I can't see any reason for the vent to get blocked on its own but could imagine a partial blockage below the top flat making it look like the vent was obstructed.
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