What was found
LOST PRESSURIZATION WHILE CLIMBING THROUGH 33,000FT. GOT CABIN ALT WARNING ASKED FOR DESCENT TO 10,000 CABIN CLIMBED TO 15,000 WHILE RUNNING QRC DONNED O2 MASK. DESCENDED TO 10,000 CABIN ALTITUDE STABILIZED AT 5,000 FT. INSPECTED AIRCRAFT AND FOUND AFT LAV DUMP VALVE TO BE PARTIAL OPENSECURED AFT LAV DUMP VALVE. PERFORMED CABIN DEPRESSURIZATION INSP AS PER B737 AMM 05-51-81, NO OTHER DEFECTS NOTED AT THIS TIME.