slow flushing toilet - is it the vent?

[fergusmcfergle]

Hi all! Hoping to get some advice:

We have a slow flushing toilet that I've tried plunging, snaking and chemicals to get going but all of that made no difference. I noticed that if I detached the U-bend from the sink that goes to the same drain the toilet flushed perfectly - this led me to think that the issue was a blocked roof vent since the fact that air could rush in to the waste pipe made all the difference. But - we have an upstairs toilet that is flushing perfectly. The upstairs toilet drains into the only visible waste pipe on the building - the non-flushing ground floor toilet is physically close to the same waste pipe so I assume it joins it somewhere underground.

The fact that another toilet draining in the same place is able to flush perfectly well seems at odds with my hypothesis of a blocked roof vent. Anybody have any ideas as to what could be going on or what I could check?

 

[Aire]

Blocked/partially blocked drains?

 

[snowhead]

Agree with above, there's a blockage you aren't moving, in the downstairs pipe.

Has the WC been O.K in the past?

When you say the air was rushing in when the U bend was off the sink, did you feel it suck air in?
If not take the U bend off and put Cling film over the pipe, flush the affected W.C.
If the cling film blows out , you've got a blockage as previously stated.

 

[Burger]

Could have something stuck on the back of the wc pan outlet?