Here is the 4" tee I found to fit the drainage tube.
I turned it up on its end to direct the main air flow to the northwest side of the foundation, as I expect it will be colder there. I can always balance it out if I need to, but we will see how it goes. I have again taped the open end to keep out water and critters.
Here I am digging out an 18" wide trench for the foundation stone. The trench will slope slightly toward the back of my property for drainage into the ditch. I plan to catch most of the water that falls on the greenhouse, but I expect there will be yard runoff.
Next, I plan to line the trench with landscape fabric, then 4" of stone and the blocks for the base. Another weekend and almost ready to build!