The filling of a storage tank or truck tank in a way that causes product to enter the vessel below the liquid level.
For example, use of a drop tube in a storage tank permits a submerged fill. Product flows into the tube and emerges at a point near the bottom of the tank. Very quickly, the liquid level will rise above this point. As a consequence, most of the product entering the tank does not splash; instead, it flows in beneath the liquid level.
This greatly reduces turbulence and therefore reduces the outflow of vapors into the atmosphere. Bottom loading of tanks or tank vehicles is a form of submerged fill.