As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER DEPARTING ORD FA'S CALLED AND INMORMED US THAT THE TANK FULL FAULT LIGHT WAS ILLUMINATED ON AFT FA PANEL BOTH LAVS WOULD NOT FLUSH. DIVERTED AND REMOVED FROM SERVICE. CYCLED POWER ON AIRCRAFT AND ALL LAVS FLUSH NORMAL. RESERVICED LAV AND C/W AMM TASK 38-32-00-710-801-A STEP 6 A ( 1-6) OPS CHECK GOOD NO OTHER DEFECTS NOTED. LATER REPLACED WASTE WATER TANK UPPER FULL LEVEL SENSOR AND CLEANED C/P ONJ WATER WASTE SYSTEM CONTROLLER. OPS AND LEAK CHECK GOOD IAW E175 AMM 35-32-00-710-801-A. RETURNED TO SERVICE.