A technique facilitates selectively disengaging a running string from a lateral tube assembly. The running string comprises a running sub which is engageable with the lateral tube assembly. The running string further comprises a window finder which is positioned to extend into a main bore casing window when the running string is deployed downhole with the lateral tube assembly. Additionally, the running string comprises an extension sub which is coupled to the window finder. The extension sub is selectively extensible to disengage the window finder from the main bore casing prior to release of the running sub from the lateral tube assembly via a release force applied through the running string.