singlepart to multipart to bigger singlepart

I remember in AV 3.3 it was possible.
Problem is:
I have waterwork network consists from mains and connections. They are all built from many short sections.
After dissolve_multipart i get two features: mains and connections.
After multipart to sinlepart (or explode or multipart to sinlepart in Xtools) I get the same state shapefile as at the beginning.
It is no t good, because I want the sections which are connected and have the same attribute is one feature (multiline).
How can I do that?