Why when flushed does my downstairs toilet take all the water away?

I would be checking the drains first.

richard
August 2009

Downstairs toilets are quite often connected directly into the drains rather than via a soil and vent pipe
(large 4inch pipe often outside). Or if it is a new problem you could have a blocked or stuck air admittance valve on an internal stub stack.

Bored Plumber
August 2009