If anyone is trying to locate the evaporator drain in a Y34 (2003-2004 M45), don't waste your time looking in the engine compartment. It does not come through the firewall. It exits the evap/heater core case on the interior driver's side (LH drive) near the accelerator pedal. You can pull the carpet back to expose the drain line. It actually travels from the HVAC case to the floor pan and then exits the vehicle through the unibody frame near the front of the driver's seat. There is a short 3" drain line that comes out of the case then via a T-fitting connects to the remainder of the drain lines. Nissan utilized a main drain line and an overflow line in case the main line gets clogged. There is a plastic plug that you can remove to see the end of the drain line on the underside of the vehicle. There are three plugs in a row and it is the one closest to the front of the vehicle. If using an evaporator coil cleaner, I recommend disconnecting the the T-fitting near the case and introducing the foam there. Otherwise you will be sending foam up a 30" drain line that may or may not make it to the evaporator coils.

Thanks for posting this!