Talking of pigs in a food processing plant brings to mind an abattoir or a plant in a really sad state of cleanliness. However, this pig is actually behind new operations in Food Processing that improve hygine while saving capacity, chemical, product and water. The principle is explained in this video
I remember first hearing of pipeline pigs when the petroleum pipeline from Durban to Johannesburg was installed. This was basically a rigid plug with the diameter of the pipeline that is pumped through the pipeline between two different fluids. The novelty here is a flexible plug which can even separate fluids in a heat exchanger. The second video demonstrates the process although the transition back to process flow is somewhat spoiled by a demo failure.
While both this videos feature the Food Process Engineering company GEA, this is not to imply they are the only or a preferred supplier. The links below are to other online starting points, but it would be wise to approach your suppliers for further information.