Now that the trench is dug we ordered rock to fill it with, we got quotes from multiple places and decided to go with crushed concrete. For a French Drain you need 1/4 in or bigger rocks to make sure that the water can travel around the rocks to the perforated pipe. We gave them the dimensions of the trench and they recommended 17 yards of stone!
Here’s the truck that delivered them (it was supposed to drop the rock in the alley driveway but the truck wouldn’t fit)
We had better pick up the pace before we get in trouble for having a pile of rocks on the street!