Sensing level of submerged solids. At least some of the example embodiments are methods including: inserting a level sensing apparatus through an aperture at a top of a reservoir such that a bottom end of an inner tube abuts an upper surface of the submerged solids in the reservoir; utilizing the submerged solids such that the upper surface of the submerged solids recedes and the level sensing apparatus moves downward with the receding upper surface of the submerged solids; constraining downward movement of an outer tube when the upper surface of the submerged solids reaches a predetermined low level; and as the upper surface of the submerged solids continues to recede, sensing relative movement of the outer tube and an inner tube as an indication that the upper surface of the submerged solids is below the predetermined low level.