What size wrench do I need to remove home water heater TPRV?

I'm trying to remove the temperature and pressure relief valve of a water heater.

The problem I'm having at this point is the actual removal of the valve from the heater unit.

I've removed the copper outflow pipe, and am left with only the brass valve itself. I've unloaded nearly an entire 4oz of PB-blaster (per the suggestion of someone at the big box home store), and still nothing. I've even tapped around the entire area with a soft mallet. I have managed to shear off half of the female outlet stem from the side of the valve.

My main issue is that I cannot grip the valve. I've tried flat and angled beaks, screw and slip-adjust (pardon my lack of technical names) wrenches, but nothing will grip the brass valve to allow me to gain any traction — they all just slip off.

I think I need something with a longer beak, or maybe I need to wrap the valve itself in something so I can grip it. I've considered the self-tightening rubber wrap wrenches, but I'm not sure that's going to provide any help, especially with the outlet stem still partially there.

I've also read I could wrap the stem area directly against the heater unit with a wet rag, and then apply some brief flame to the end area of the valve, and that this should help loosen things.

This is supposed to be easy enough to do w/o calling in a plumber, and I suspect it is if I'm using the proper tools. Can you please provide some assistance? Specific names/sizes/models are more useful than "get a big wrench".

Thank you for any help you can send my way!