it is always good to test an assortment of cartos, different juices have different viscosities, and may not wick well in some carts as well as others. try putting in a thinner liquid to see if that alleviates your problem. is the hole too small? you may be starving the carto. there are quite a few threads on this subject. try to fill just the carto, to see if its a
juice feeding issue...
only way to keep a tank from sliding as far as i am aware of is to use a wide drip tip, such as the MING or PAWN(personal choice). that would add some extra resistance to keep the tank from sliding off the carto (the only reason i dont use those style tanks). Adding a thicker o-ring to the inside of the tank has helped make it a snugger fit.
the hole of the carto should be placed near the bottom , but not too low where the tank is covering the hole.