A plunger keeps the sampler closed until it strikes the bottom of the tank, then the sampler fills. When raised, the plunger automatically falls back into position, closes the sampler, and prevents any contamination by liquid taken at a higher level. This device picks up sediment or water directly off the bottom of the tank.

But a sample can be taken at any point above the bottom by attaching a cable to the top of the plunger, raising it at will to fill the sampler and lowering it to close the sampler. However, average sampling operations cannot be performed with the perfect control possible with the average model.