The Air Operated Diaphragm Pumps (AOD) are the kings when incomes to moving liquid with suspended solids. The 3/4" Yamada NDP-20 AOD can move solid rocks up to 2 mm; the 1/2" pump can move solids up to 1mm. AODs can be run dry and are not harmed if they stall. They do have disadvantages though as they require compressed air to operate, are noiser, and do not provide as smooth of a flow as an impellor pump.