Null structures are being replaced

[Anonymous]

I have created my own parts list. The parts list I have created only has the null structure in it and a 4" pvc pipe.
When I creat a network from layout this works perfectly but when I creat from an object (A 3d polyline that I used to get the elevations off the surface) it inserts the right water but pulls in a drop inlet structure. I have no idea where this structure is comming from. the rules I have set up for the null structures will not work be cause the drop inlets are using a different rules set. Does anyone know were the structures are coming from. like I said the only structure in my network parts list is a null structure and this null structure is set to follow the set of rules I have created for it.