For flushing analysis, it is best to start from an all-pipe model. Small pipes without a means of flushing (e.g. 2 in. pipes) can be excluded. Ideally, the model will also contain every hydrant and isolating valve at its exact location. This is especially important for UDF because the location of a hydrant relative to the closed valves is very important.

If a model does not contain hydrant elements, junction nodes can be used as flushing points. The error should be small for conventional flushing although for UDF a valve may be closed between the hydrant and junction. If hydrant elements are used, it is not necessary in explicitly include the hydrant lateral in the model because the lateral length and its associated head losses can be accounted for within the hydrant element.

If isolating valves are not included in the model, the user can simulate valve closing by closing pipes, although it is up to the user to insure that a valve is actually available in the field to close the pipe.