Can PVC drain lines be on the ground/dirt in the crawlspace or do they have to be suspended above the ground. The lot has a great slope in front to back so the plumber just layed the drain with the natural slope of the yard to the city connection.
They need to be properly "supported" and "secured".
Sounds like they have the "supported" part down. If the line was buried, then it would also be "secured".
Are you in a freeze area? If so, it needs to be protected against freezing too.