The overflow system is the last line of defense against the excessive container filling. An overflow system consists of an overflow nozzle with internal and/or external piping and, in some cases, a siphon breaker. In this context, the container could be an atmospheric tank or a non-flooded vessel. However, not all the containers need an overflow system. If siphoning the liquid out of the container is not affordable, or if the other protective layers against overfilling provide sufficient coverage, an overflow system may not be necessary. In general practice, atmospheric tanksbut not vesselshave overflow systems.