Pumping and filtration are big challenges–the plastic media we use is an industrial abrasive. Great for modeling, hell on pumps. Pumps are complex devices with characteristics narrowly constrained for particular uses. We’ve tested dozens of pumps over the years and destroyed quite a few. You won’t find a “River Model Mark IV” in any catalog.
We had good news from a plastic media supplier today, we’ve broken yet another barrier and will be getting our plastic river modeling media color-coded by size. Like the pump search, this has taken years.