As mentioned, lightly blowing the excess out will usually do the trick. In the year and a half that I've been using tanks, I've had maybe 5 cartos that flooded fairly consistently but I was able to fix them all. My first step is to lightly blow the juice out and then do a couple of hits with an extremely light pull. That works most of the time. If that doesn't do the trick, I'll try to repressurize the tank by either (a) pulling the carto down to allow air into (or out of) the tank and then slowly reseating it, or (b) holding the tank upside down while I take a hit or two. If your cartos have two holes, you can always break a toothpick off in one of them as a method of juice control... I've only had to do this once.
One thing to keep in mind is that removing/connecting some drip tips can cause flooding as well. My favorite SS drip tip does this for some reason. Every time I connect it, juice is pulled into the carto (which is evident from the bubbles). I'm actually sort of baffled by this since the drip tip has a fairly wide opening... I can't see why it would cause any fluctuation in pressure within the carto/tank.