What was found
ACID SMELL ("DIRTY SOCKS SMELL") REPORTED BY CABIN CREW AND NOTICED BY CREW DURING TAXI OUT. FLIGHT RETURNED TO THE GATE. MX ACCOMPLISHED JC 26L00021001-TROUBLESHOOTING CABIN AIR QUALITY AND ACCOMPLISHED JC 26L00021002 - APU SMELL IN CABIN AND ACCOMPLISHED JC 26L00021004 - DECONTAMINATION OF THE ENVIRONMENTAL CONTROL SYS A319/A320/A321 (ENGINES & APU) AND ACCOMPLISHED JC 26L31049009 -CLEAN APU COND COMPRESSOR. FOUND APU OIL CAP LOOSE. TIGHTENED OIL CAP.