I have a clogged heater core in my 2002 Elantra GT. I want to try reverse flushing just the heater core. My question is, which tube is the inlet and which is the outlet? Is it inlet (passenger side), outlet (driver side) or the opposite? also, has anyone ever successfully reverse flushed a heater core? Thanks.

The local shop I took it to says it has to be replaced and they want $1200 to do it...

 

It appears to flow in the passenger side and out the driver side:

 

perfect. thank you. really appreciate it!