How can you limit the design of a conduit so that certain conduit sizes are not included?
If you want to put a maximum size to the Design run, the simplest method would be to open the Default Design Constraints dialog. Go to the Gravity Pipe tab. On the right, select the Section Size tab. Select "Limit Section Size" and enter a value for the maximum size of the pipe.
If you want to make sure you do not include small pipes or if there are pipes in the catalog conduit that should not be included in the design run, open the catalog conduit by going to Components > Conduit Catalog. This shows all available conduits of the catalog item. If you want to only include certain ones for the design run, uncheck the item from the "Available for Design" column. If you uncheck these, they will not be included in the design run.