I hope someone can explain the odd behaviour of my downstairs loo.
After it is flushed the water level slowly drops a few inches.
The only explanation I can think of is that the pressure in the drain
is lower than atmospheric and the water is "sucked" out.
I can't understand how this can happen. Surely the drain is open to
the atmosphere somewhere? And why only the downstairs loo?
(i) its blocked, and teh als bit gently seeps through.
(ii) the soils tsack vent is blocked, leading to vaccuum in teh pipe as
thre should be an open ended pipe or air admittance valve in teh pipe
above the loo somewhere to stop this.
Not (i) as the water level ends up a couple of inches below normal. (I
should have explained better.)
So must be (ii). I'll have to look and see if there is "one of those
pipes that goes up to the roof, then has an elabotate anti-birds-nest
thingmy". Still don't see how there would be a vacuum in there...
When you flush the bog, the plug of water (and any
(umm) effluvium), effectively becomes a temporary
descending piston in the vertical pipe. The vent
at the top of the vertical pipe allows air in, so
that the piston does not pull a vacuum on the water
in the bowl of the bog.
Ok I can understand that. But (and I should have mentioned this in the
original post) if, say 1/2 hour after I last flushed it, I pour a jug
of water in very slowly - it gets sucked out.
Also, there is no "big pipe going up to above the roof" for the
downstairs loo, so I guess that there is "some other arrangement" and
that it's blocked. What should I be looking for? I guess a pipe
branching off the soil pipe??
You are looking for an air admitance valve. This sits on the top of the
shortened stack and just lets air in when required. They do have a tendency
Another alternative is that you have a macerator pump with small bore
drainage (i.e. Saniflo). However, you'd probably know if you had one of
these from the noise.
My final suggestion is that the toilet is design to have a lower water level
in the bowl than you are used to. A syphonic action pan may take some time
to return to its standard level.
> > Wind.
> Well it has been windy recently, so I thought this, at first. However
> it does it every time - even if it's not windy.
Just wondering -are you on mains sewer or sceptical tank ?
I experience a similar phenomenon of low level with my loo when the
inpection pit between
the bog and the tank starts to fill with effluent due to a faulty pipe
blocking, between pit and tank.
I then now that its time to get the rods ready to clear matters as the
next stage is
downstairs toilet overflowing.
I suppose that a similar thing could happen even if on mains sewers if the
pit fills with effluent.
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