I'm glad my experience is proving helpful to someone!
I think the vac line in question is the line going to the purge valve, which is up in the V of the engine. I disconnected the engine side and the charcoal canister side and blew compressed air through it to clear it out.
regarding pressurizing the tank, yes I believe you can definitely damage something by over doing it. And by all means, only use a manual pump that does not create any spark whatsoever, after all this is a fuel tank that could definitely cause you a big problem otherwise. I used a cheapo fluid pump from the auto part store, and I used the line coming off the evap canister only because i'd already replaced the hose going to it with a radiator hose (saw someone else give that advice when starting my search about this problem). All those OEM lines have the fittings on the end that would make it hard to get a seal, the hose I replaced worked awesome for this. You should be able to use whatever line you want to though.
I didn't pressurize very much at all. But I repeated the cycle probably 20 times until almost nothing was coming out any more. Start out very light, see how it goes and judge if you need to go heavier. But yes, I believe you could damage a seal if you go to hard, I wouldn't recommend compressed air at all. The fluid pump allowed me the confidence to know that I wouldn't over do it.
