B737-800
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Aircraft Equipment Problem Less Severe; Ground Event / Encounter Fuel Issue
General Release Refused / Aircraft Not Accepted
Aircraft; Human Factors
B737; ZZZ [Airport]; Gate XXX: Fuel reported leaking from the refuel manifold following ground refueling. Maintenance discovered rag/cloth fragments protruding from the manifold poppet valve. This prevented closure of the valve and resultant leak. I suspected the debris came from the ground refuel pit or truck during the refueling process and that there could be additional contaminates in the aircraft fuel tanks. Consequently; I refused the aircraft. The following day I reviewed the aircraft electronic logbook and discovered that the aircraft was returned to service without inspection of the fuel tanks. This is an unsatisfactory decision.  Aircraft fuel tanks should be examined for debris and refuel pit/truck should be inspected to determine source of possibly contaminated fuel.
B737-800 pilot reported refusing an aircraft after it was found to be leaking fuel from the refuel manifold.  Maintenance discovered rag cloth fragments protruding from the poppet valve which reportedly prevented proper closure of the valve.