One way valves in {TAIL ~ the bottom} of the dipper allow {HEAD ~ water} to pass into the dipper 
One way valves in { TAIL ~ the bottom } of the dipper allow { HEAD ~ water } to pass into the dipper
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH