No, you won't get all of the money back and they will get a cut, but you can now focus your energy on things that generate new revenue as opposed to wasting your resources (time, energy, money) chasing old money. 

If customers just need 1-2 months, they don't want to have to hook up water and other services.More and more of the big operators are doing the same as you and taking a cut of the water, electricity, internet, security, etc.

Now she wants a cut of the rent, but I still get to sleep with her. 

If they are buying, selling, or investing in real estate maybe you can get a cut of that. 

This way you get the best service, get a cut, and can't screw it up.

This would be a great chance to allow them to bring their knowledge of deal execution, while you soak up the process & get a cut of the profits. 

After estimating the overage you then approach the previous owner and tell them that you can help them get the overage if they agree to give you a cut?

Heck in my area most guys were still doing cesspools in 1957 let alone acutal septic tanks with dboxes and leachfeilds. 

They shouldn't be working for a cut of the deal. 

We dont do K-12 anymore because that is a cut throat business these days.