Good Morning,
Thank you for your enquiry, you would need to measure your water line in your cistern.
For example, if your water line is measuring 7" you would need to add an extra inch on top of the height you require for the internal overflow to work, therefore you would need to purchase an 8" syphon.
I hope this information help.
Kindest Regards
Thomas Dudley Sales Team
Answered by: Dudley Sales TDL
Date published: 2020-12-14