My 2000 S70 2.4 threw a code for the fuel tank pressure sensor. When I went to fuel up, it wouldn't accept it at full flow (clicked off when I squeezed the pump handle all the way) and I had to add it a little at a time, so yeah, there seems to be something awry. Should I start with the evap system, and if so, where do I look first? The car's been sitting for a while, had a big rodent nest on top of the engine, now gone, starts and runs ok. And where might that sensor be located?

Check the purge valve, on the radiator shroud. It might need replacing and fix the code at the same time. A 9V battery touched to the purge valve leads should open/close the valve.

At least it is easy to get to.

As for pumping in gas, the cannister is probably full of liquid gasoline and not allowing air to escape the tank. A couple of 1/2 tank fill ups should resolve that if the purge valve is replaced. NEVER fill the tank past the pump automatic shutoff, the extra fuel will just drain to the cannister and be wasted.
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Keeping it running is better than buying new

The purge valve clicks ok with the 9v trick. Didn't blow in the hose to check, but guessing if it makes a noise something's moving inside. Is the valve at the evap canister the next thing to check?

Also, last fillup wasn't a problem. I and the last owner never topped it up, but there's a remote possibility an Oregon pump jockey may have done.(can't pump your own there.) It's been a while since I addressed this issue, and have been driving so little I've only gotten gas a few times this year.

I suggest that when you stop for gas in Oregon, just tell the attendant you want 15 gallons or something shy of 'topping it off'. The fuel gauge is in 6 gallon increments. People in NJ have the same problem.
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Keeping it running is better than buying new