Liquid Fillers can be manufactured to allow bottom up filling of containers by using an air over oil system.  The air over oil system allows diving head nozzles to enter the container prior to filling.  The fill heads can then be retracted, or raised, at different speeds dependant on the needs of the product. 

The air over oil system and bottom up filling can help products, for example, that may not be of a uniform consistency or that may tend to create "caverns" or air bubbles in the supply tank.  Filling machines can also control some foamy products by utilizing an air over oil system and bottom up filling.