If you're just riding for fun, I honestly wouldn't worry about it - if you're racing, I definitely would.
Gas in a dirtbike gas tank (i.e., not an airtight container) will still be good after a month just by itself, especially if it's good quality gas. Adding Stabil (or similar) slows the oxidation of the fuel and depending on temperature and humidity (more of both is worse), gas in a gas tank should be good for at least a few months. I'm in the military and deployed right now - it'll have been about four months by the time I get home to my bike. I use Stabil when I'm going to be gone for a while, leave the tank mostly full, add a little fresh gas when I get back, and have no issues with it whatsoever. Stabil basically keeps gas volatile for a longer period of time. If you store gas in a sealed container with Stabil, it'll probably last a good two years or more.
All this said, it'll do wonders to at least start up and run the bike once in awhile if you can to keep the fuel/oil flowing at least a little bit.
Anyway, I have a carbureted bike and to remove gas, I just remove the tank and dump it out. I don't know that it should be any different for a tank with a fuel pump in the bottom of it (aside from having to disconnect wires), but someone else will have to weigh in on that.