Wynne, welcome to PB. I'm certian someone with knowledge of legal and health laws will chime in. Ewest? I am sure there are regulations/laws concerning discharge of raw sewage. Also am assuming that each state and/or county has it's individual restraints. I would check with the county health dept. If no results from them maybe at the state or federal level. Approach the neighbors with friendly/neighborly requests, probably gonna have to deal with them long term.
Good luck, Bob-O

Do nature a favor, spay/neuter your pets and any weird friends or relatives.