So many different types of PVC piping. I'm building an RV space approx: 300' away from my septic tank and need to know exactly which type of sch 40 PVC to use for the sewer line... Lowe's want to know; under pressure or not, will the fitting be under pressure or not, how will you be building the cleanouts?? AHHHHHHHHHHH!! All I know is that it will be buried and need some cleanout in there... HELP!!