Stormwater easement for newly built property

Has anyone tried talk to down stream neighbours to get a storm water easement on neighbour's property?
How much on average does one pay to neighbour to get their approval to put a storm water easement?
Thanks in advance.

Background:
To get council's approval on a subdivision DA, council requires me to demonstrate that storm water can be drained to the nearest council's storm water pipes.

 

I haven't done this personally but lived in a townhouse where the developer had negotiated an easement with the neighbour in the property directly behind ours. Not sure if it helps but the developer paid $30,000 to the neighbour to get this done.

I only know this because later on that site was developed and the new developer wanted to move the easement so he could build his townhouses on top of where it was previously located. We charged him $50,000 to move it

vtt

 

I don't actually know the answer, but I think it will all depend on what the area could be used for. If it is large enough to put a development or even extend the house then it will be worth more than what it would if it looks like it would only ever be used as a garden or backyard.