How to Measure a Toilet Lever Flush Syphon

When replacing a lever flush syphon, it isn't a "one size fits all" type scenario. There are many different sizes and shapes available and it's important to make sure that the syphon you're installing is suitable for the cistern.

If your syphon is too small for the cistern then the water level in the cistern would need to be reduced, as many modern syphons feature an internal overflow (usually just below the cap on the top). Reducing the water level in the cistern would ultimately lead to a large reduction in flush volume.

If the syphon is too tall, you may not be able to secure the cistern lid. The internal overflow may also be too high which in extreme circumstances may result in the cistern overflowing completely if there is no additional overflow tube.

Most syphons range in size from 7.5" to 10.5". The way to measure most syphons is to start at the bottom of the bell housing and measure up to the lip of the cap on top of the syphon. Our measuring guide below illustrates the points at which to measure your syphon.