No straw is needed. If you find that it isn't wicking, take it out and trim a tiny bit off of one edge (that is cut wider than the cartridge).
You are better off to cut it a bit too wide rather than not wide enough (then it may leak). You only need to compress the foam in one direction (width) so cut the width just slightly larger and the depth and length the same size as the cart.
If you use VG liquid that is thick, it may absorb a bit more slowly with the foam and seem to want to pool. It will soak in, but will do so a bit more slowly. I find a small 2 dram glass dropper can help to force VG fluids
through foam fillers.
I've used one piece for well over 4 months. If I think it needs it, I'll rinse it out and put it back in so no need to
throw it away for quite a while. Let us know how it goes!