The basic concept in flushing is an "Event". This corresponds to one snapshot during a flushing program. Flushing analysis consists of simulating many flushing events.

WaterGEMS CONNECT can analyze two general types of flushing, Conventional and unidirectional:

• Conventional flushing consists of opening up hydrants or blowoffs one at a time without any isolation valve operation.
• unidirectional flushing (UDF) consists of one or more hydrants or blowoffs while isolation valves (or pipes) may be closed to control the direction of flow.

Depending on the target velocities and layout of the system, conventional flushing is often adequate. unidirectional flushing will improve velocity although it requires additional labor. A recommended workflow is to first simulate conventional flushing and then identify areas which are not adequately flushed and require unidirectional flushing. If a secondary goal is to test the operation of every hydrant, then conventional flushing is usually adequate while if valve exercising is also a goal, unidirectional flushing becomes more attractive.