The downstairs toilet used to flush OK but now the bowl fills with water and then takes about five seconds to drain away, the water level dropping about 3 cm below normal and slowly rising again to about 1 cm below normal.
It seems to me that there must be a partial blockage somewhere, and I'd prefer to sort it out before it becomes a total blockage. Any suggestions?
From the back of the pan the pipe turns right, goes through a side wall, then turns right again and goes into the side of a vertical soil stack (total distance so far about 1 metre). The soil stack is only about a metre long, being capped just above the junction. This unusual (and possibly illegal) arrangement hasn't given any trouble before in the 15 years we've lived here.