No problem, EXTRAN doesn't mind modeling the saggy parts of a sewer
reach. Do your best to match the sags with additional nodes & links.

I'm not sure about your "bolt-down lid" option. If the sewer is pretty
deep you can just set the node ground elevation to the actual ground
elev and let EXTRAN handle the pressure flow. If it's not very deep and
surface flooding is expected, you might need to represent the surface
overflow and storage properties.

Michael A. Gregory, P.E.
GregoryMA@CDM.COM