Way leave Agreement for use of neighbours drain

Hankins1

Afternoon,
We have a verbal agreement from our neighbour that he is happy for our rain water from an extension to run through his drain, before exiting via a field drain.
We need it in writing for building control to go with our proposed plans but we are a bit lost as to the exact wording of this document.
Does anyone have experience of this or know where I could steal a template document from ?
We are in Scotland.
It will be put on the deeds via a solicitor at a later date it is purely for planning at this current stage.
Many Thanks in advance.
Hankins1.