Does anyone else have trouble with the build-up of dust in these U-shaped PVC feeders? We made a couple, and while I like the idea of them, the one with crumbles doesn't work well. First, the feed doesn't seem to flow as well as the one with pellets. And second, there's always such a build-up of dust from crumbles that I have to scoop it out by hand to expose more of the crumbles. I have this trouble in regular store-bought feeders, too, but I have yet to find crumbles that don't have a lot of dust in them. Any thoughts on how to alleviate this problem? We're thinking of cutting out the bottom of the horizontal tube and replacing it with screen in hopes the dust will fall through but are worried this will cause more friction and restrict the flow of the feed even more.