An apparatus for draining reservoirs includes a pump disposed in contact with a lower surface of the vessel to be drained, wherein the pump is connected to a discharge pipe inserted into the vessel through an insertion tube connected to a retrofit assembly of the vessel. The apparatus also includes seals within the insertion tube and within the discharge pipe to prevent gases from within the vessel from passing through the insertion tube and discharge pipe and into the atmosphere. An expansion joint unit attaches to the discharge pipe to prevent the rotation of the pump relative to the discharge pipe. The expansion joint unit also maintains the pump in substantial contact with the lower surface of the vessel even when thermal expansion causes the vessel to expand and the position of the discharge pipe to lift.