As a visualization of liquid flow, I think it would be funny to have a large room into which many tennis balls are emptied. The tennis balls would represent the individual particles, which bounce and jostle against each other to produce the ultimate effect of the liquid. When everything has come to a rest, a large door on one side could be opened to drain the room in a comedic fashion.
Pipe flow is more poorly understood (and of interest to oil companies and other big concerns), but making a pipe-shaped room is a tad impractical, I think. Would be worth filming, though.