AH, HA You assume the operation is legit!! A call to the county health dept can verify this. When I started work at the Health Dept there were a couple pumpers causing serious problems with their dumping. This situation became a health priority and ended with one individual serving a jail term and the other going out of business. Unless you have knowledge otherwise - do not assume the operation is legit. The local health dept should have knowledge of this operation. And yes, in more urban areas it is normal that the "load" be taken to the local sewage treatment facility for processing.
Part of living in the county is and will always be - unusual sewage disposal practices - not previously experienced by urban folks - - large operations raising animals, be it horses, cows, pigs etc and even sewage disposal facilities. All of these practices are legislated to the rural areas by our elected officials because urban folks don't really appreciate the activities.