I am installing an interior perimeter drain in a damp outbuilding crawl space. In the "literature" (YouTube) this kind of drain is commonly described but always with a pumped discharge (basin, pump, 1 1/2" SCH-40 PVC pipe with check valve, exiting above grade). However in my case since I am constructing an adjacent trenched drain outside, and I would like to avoid the reliability issues associated with pumps, I would like to "gravity" drain the system. At first glance this is easy to achieve: I dig under the foundation footer next to the interior drain pipe to reach the exterior trenched outflow pipe and connect the two. However I suspect a more complex arrangement is required, including some kind of catch basin and/or clean-out risers. This is my question: what's the "correct" plumbing fixture setup for this situation? I've marked the diagram below: question is what to install at points A and B?

crawl space drain cross section diagram

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