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Water level in toilet pan low after flushing and refilling - why?

The main drain had broken. Whilst awaiting repair, the drain had to be rodded through 3 times. Following the final rodding, I noticed that the water level in the toilet pan - after flushing - is not returning to the level it used to. It is about an inch lower than normal. I had the drain checked again and it seems to be clear and running normally. The toilet is filling and flushing normally - it is just after flushing the water in the pan is lower than it should be - about an inch down on normal.

At the same time, the sink (which uses the same drain system) is occasionally giving back 'unpleasant fumes.'

Both toilet and sink are located downstairs. I don't know the make and model numbers - they are both about 15 years old. The house is 60 years old and has a 'clay' drain (not plastic).

Donna Walker
February 2008

D.I.Y, Toilets Water Toilet Drain

If there is a partial blockage in the waste pipe - even some distance away from the toilet/sink - it will act as a venturi and cause suction on the waste pipe side of the traps causing the water to be sucked out. If the height difference is not sufficient and/or the suction is high enough, the water can be pulled away from the trap, allowing odours from the waste pipe to come into the house.

Sandman
February 2008

The level of water left in the pan is determined by the height of the bottom of the waste outlet. My guess is that now the drains are clear the level is correct. It may have been higher before because of the blockage.
As to the sink, it would be worth removing and cleaning the U bend or water trap. The trap is there to minimise bad odours coming back from the drains.

Colin
February 2008