I have a couple of litter catching mats for one of the litter boxes (the other one is a top entry so the mat isn't necessary) and I find that getting the caught litter out of the mat to be impossible. It just feels like there will always be stuff coming out of it no matter how hard I try. Is there a trick to "emptying" these mats more efficiently? Today I laid them upside down on my kitchen floor and pounded them several times, but again, there was still a lot coming out when I put them back.