Even if you don't have one of those IBtanked "thingies" ... if you have something like a small pill bottle from a pharmacy that doesn't have a childproof cap, that your cartotank will fit into, that might also work to force the air out of the carto -- when you tighten the cap, you should see air bubbles escaping from the carto; do it several times, until there's a bit of juice in the bottom of the pill bottle.
Andria
I think I have a couple bottles that may work - I'll give that a try. Thanks!