I use a filler that I don't think others are using. I use tissues that are the thick cotton tissues for cleaning eye glasses. They have no scent or coloring. I had some from LenCrafters when I got glasses there. I cut about a 1 in x 2 in rectangle, roll it up like the PTB, fold it in half, put a correctly cut coffee straw along one side, point down, and insert with fold-end first into the cart. The straw should be just below the opening of the cart. Then I cut straight across with sharp scissors, so the filler is flush with the opening, not just below it like others do with the PTB. Best wicking filler I have found. Imparts no flavor itself. I find it works better than the PTB, but still props to the inventor of that, as without the PTB method, I would not have come up with this. The tissues are not paper, they are cotton I believe.
Others use Walmart fluval, which is similar to the poly fill that comes stock.
Kurt