Don't know anything about the ACJ, but on the BBJ the auxiliary tank system is usually installed under a(an?) STC by PATS. A quick Google search threw up this..
http://www.patsaircraft.com/prodnser...fictaions.html.
A simplified description can also be found on Capt. Chris Brady's B737 website, the URL to the auxiliary fuel system..
http://www.b737.org.uk/fuel.htm#Auxiliary_Fuel_System
HTH