An apparatus for retaining fluid in a pipe includes an elongated body adapted to be positioned within a subsea wellhead assembly. The elongated body has an end adapted for connection to the pipe, a flow passage for fluid communication with the pipe, and an outer surface for engagement with a sealing member in the subsea wellhead assembly. A first chamber is defined within the elongated body and connected to receive pressure from above the subsea wellhead assembly. A second chamber is defined within the elongated body and connected to receive pressure from below the subsea wellhead assembly. A valve is supported in the elongated body for movement in response to pressure differential between the first and the second chambers. The valve is movable between an open position to permit fluid flow through the flow passage and a closed position to prevent fluid flow through the flow passage.