I'm thinking they are still wet.
I clean my cartos often (to change flavors, or just when they "marshmallow" on me.)
I wish I could find the video now. It's a man from Australia using this method, but he uses water.
I take a 5ml syringe and put the inner clear round cap on the end. Put it in the carto, so the clear ring makes a seal. Use the syringe to pull
VODKA thru and squirt it back out. Repeat several times.
When you feel like you're done, take the syringe tip out of the vodka and pull and push to get the liquid out. Blow through very had a couple times.
GENTLY dry burn on and off for a few minutes.
Fill...enjoy.
The vodka dries quickly and you don't have to wait for 4 days for the water to dry out.