Appreciate your advice.
I am installing a septic leach drain for a septic which just found had for the last 20 years had been piping a few metres off side of steep hill. I have dug a 10m long by .6m wide ditch at an approx depth of 4 ft. Am I correct in the following: 2 ft depth of 20mm blue aggregate with pipe in the middle covered by tar paper with top 2 ft of dirt? This info I gained from the internet.

Assuming above is correct, is it better/worse/same to use the flexible slotted 100mm poly pipe as opposed to the PVC pipe with slots? (Bunnings guy said poly is fine). Should I be putting some sand on top of tar paper rather than the dirt (clay type)? Should I cap the end of the pipe or have it "open" down steep hill?

Thanks.