Abstract: A fluid flow sampler having a peristaltic pump which periodically draws a sample volume of effluent from a sewer main through a supply line to a collecting chamber wherein the pH is recorded after which the sampled effluent is transferred to an agitated and cooled holding chamber. The supply lines are valve controlled to delay delivery to the collecting chamber until steady state conditions are achieved in the supply line. The supply lines are air purged when the pump is not operating and lines are underground which are connected to a sampler inside a building thereby eliminating line freezing. The entire operation of obtaining, holding and maintaining the representative samples is programable and completely automatic.