Haven't used Caswell, but for Redkote or POR15 I use a pipe cleaner to clear them when I first coat. You can't leave it in -- it'll be stuck -- and you've got to go back and swipe it through periodically as it cures to keep the passages clear. I learned the hard way -- I cleared passages a couple times, but not enough, and had a clogged one. I wound up just cutting it off at the bend and drilling through the straight part. Shitty tank, didn't matter, fuel hose made the bend. Don't forget to tape off your tank.