One of my projects: "THEY" told me I just needed a 6" perforated pipe. I went with 12". Figured a little overkill would given a few extra decades, when combined with the gravel and fabric.
Flooding of the basement was not a deal, until the timber was harvested from the neighboring property behind the house.
When this was done, even after a long hot spell, you could pop the top on the green access tubes and see about 4" of water running.
Just for reference, there was another vertical tube on the other end, but it was only about 4' tall, in keeping with the slop at that end. It all drained into the field in front of the house.
SIDE NOTE: I took the photo of the guy I hired from the attic. It made for a much more dramatic looking project, but that's our secret.
