Trying to get the broken ASV out of the pickup tube fitting was a fail. There's a hard metal inner lining, so even if you get a tool to bite you just spin the inner lining and the threads stay stuck.
What actually worked was soaking the pickup tube to tank fittings with PB blaster for about 10 days, and then going back and forth between gently torquing them, holding the tank fitting hex in place, and banging on the pick up tube block with a drift to break up corrosion. I spent hours doing that between PB blaster soakings, and it finally budged. I think if I move faster or more aggressively I'd likely have ruined my tank.
I'll stress the words "gently" and "patiently" , as I couldn't believe how easily the ASV broke off when I first tried to remove it.
I'm going to give these things a fresh re-torque every spring now, to keep it from happening again.