As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI CREW NOTED LARGE AMOUNT OF SMOKE FROM THE VENTIALLTION SYS. ACFT WAS STOPPED AND SHUTDOWN. UPON INSP, CREW NOTICED HYD FLUID COATING THE EXTERIOR SURFACE OF THE TAIL SECTION ON THE ACFT. MAINT DISCOVERED THE STANDBY RUDDER HYD MANIFOLD LEAKING HYD FLUID INTO THE INLET OF THE APU. THE MANIFOLD WAS REPLACED.