Cat 259D 3rd aux port

[dantran1010]

I am picking up a low hour (1100) 2014 Cat 259D S/N FTL02385 this upcoming week and trying to get in to the operation. Two questions, what is the smaller center aux port for in between the two normal aux ports in the front of the machine? (This is a NON-high flow machine and it is not the aux electrical hookup port) Secondly how are the auxiliary ports operated, the right hand scroll knob? I know there is a switch up above for continuous flow hydraulics but being new to caterpillar just to see the scroll instead of push buttons didn't make sense. Please clue me in! Tia!

 

[foton]

I have a 2017 wacker neuson sw-20 and on that machine it is a case drain line , I assume it is the same on your machine.