vent grade

As I understand it, code (at least IPC) specifies vents must slope to drain, to prevent condensation from accumulating, but it doesn't care if it slopes toward the fixture drain or toward a vent stack that slopes back to drain, as long as there aren't traps, and it slopes all the way to drain.

To avoid moving some blocking in a wall, I sloped a vent down to the vent stack, away from the fixture drain, thinking this was OK. But, now if I connect to the vent stack with an inverted santee, it will trap the condensation and break my slope. If I connect to the vent stack with the santee in the drain position, then it's not sloping up for the air flow to vent. A vent tee seems the obvious solution, yet nobody around here stocks a vent tee. They talk to me like I'm crazy.

Maybe I am

That is why inspectors WANT the vent sloping back to the fixture. You have created a conundrum for yourself if it is getting inspected.

Of course it's getting inspected. I explained the situation to the inspector, and he says I can install a santee in the drain orientation, that is, not inverted. I'll have to remember to keep my vents sloped to the fixture in the future.

YOu have one of the few intelligent inspectors. MOST insist on the tee being oriented properly because they think air uses the same dynamics as water and cannot flow through a backwards tee. THESE inspectors WILL reject a tee installed like you are going to do it.