We are a third party billing company, and deal with this question all the time.
When we are faced with this decision it usually comes down to the verbiage used on the bills.
For instance: If your charging tenants for using your infrastructure, instead of directly charging for sewer....you can use the money to maintain your septic.
We provide turn- key billing services for over 8,000 per month and the only state we've seen this not work in is in Missouri.
Good luck, I'm intrested to see what you guys end up doing.