What is this part and hose outlet and factory A/C questions

[cortcomp]

Hey all! First, great place and thanks everyone for all the comments and help on my build thread.

Second, i've been getting everything engine bay related out of the way, and i see three outlets from the AC evap box. Two have hoses and look like the normal setup i'd expect to see...third i don't know what it is and what connects to it? Some searching hasn't turned anything up.

Secondly, can i flush the evaporator? Except for that mystery tube, i don't think it's been open to air, but you never now. If so, what can/do i flush it with? And can/how do you test them? I hate to take that out and replace it, they're pricey.

I am putting a new compressor/drier/condenser and hoses (new sanden type compressor) so if there's anything else i should know, chime in!

And do hose clamps really work on an A/C system?!?!


Lastly, second picture, it fell out when i took the motor out, looks like some kind of mount cushion, only found one, can't seem to make sense where it goes. Truck catalogs don't show anything like it. Ideas?