What was found
FLT 316, SAN-IAD, ON TAXI OUT, RETURNED TO GATE, BURNING SMELL COMING FROM REAR OF LAVATORY OF AIRCRAFT. T/S RT & LT AFT LAVS. NO C/B POPPED. WATER HEATERS OK. FLUSH TIMERS OK. NO SMOKE SMELL FROM LAVS. BACK GALLEY C/B PANELS. NO POPPED C/B. FLIGHT CREW RAN ENGINES & PACKS. NO ELEC SMELL IN CABIN. OK FOR SERVICE. NO FAULTS NOTED. PERFORMED SDCU CHECK, NO FAULTS. OK FOR SERVICE PER AMM TASK 24-00-00-810-823.