Ask your contractor about that.

Ask the contractor if what he says he will do is correct?

LOL

I was always taught not to combine downspout drainpipes with sump drains, box drains, or whatever for just that reason. I also prefer using PVC sewer and drain pipe instead of the black corrugated, it's way less prone to clogging and you can (usually) just blast a clog out with a hose.

Well said. Those black corrugated drain pipes are terrible!

Thank you, everyone, for your thoughts. What you have told me pretty much lines up with what I have read before on other projects. So now I’m in a conundrum.

I did discuss it with him but he said we will use the black currugated line because we have to go around trees, hardscaping and electrical (to avoid running it through leach lines)so that made some sense to me. Part of the line will be pvc. As for the joining up of the three lines, he told me he has done thousands (?) of these projects and there should be no problem. He doesn’t want to put another line down the yard because of the leach bed and the landscaping. So I guess I will have to accept what he says. He seems competent and he sure charges enough for some ditch digging so it better work! I am learning a lot (that I don’t want to know) about septics and drainage. lol

Thanks again.