mrrunon, what type of PV/e-cig do you have? It might help to know what type of cart you're dealing with.
Also, are you using prefilled carts or carts you've filled yourself?
I'll admit, I don't 'clean' mine per say. I find even if they dry really well they're not the same and it takes a while to get back to normal. I just squeeze all the old juice out with a paper towel and roll the filler around in the towel. If it's still basically white I wipe out the inside of the cart and stuff the filler back in. That way I don't get a watered down taste.