Properly trained operators, will perform unidirectional flushing without a problem
The simplest method I have seen, is to have a map of the system and the operator(s) highlight each section starting at the source(s) toward the ends
you could use EPAnet to verify that positive pressures are maintained in areas that are hilly and/or have small piping.
EPAnet could also be used to establish minimum flush times, if the contaminates you are concerned about are not detectable in the field. I once provided this information to the crew who were flushing in a system from un-chlorinated to chlorinated, they used the times I provided to determine when to start measuring for chlorine on the longer runs. (it also assisted in fine tuning the calibration of the model by pointing out where pipe sizes were not correct on the maps.)
