My boss has designed a gravity project that has 21" PVC. Civil 3D 2010 only has 20" PVC, not 21". He basically said 21" PVC exists (JM Eagle) so make it happen. So how exactly can I add a new size to the Parts Catalog under PVC?
Under your "Create Design" tab, go into "Part Builder". Find the particular part family you're looking to edit, and modify part sizes...
Right click on "Size Parameters" and select "Edit Values"...
Select one of the part rows, then using the *New* button in the upper left, click to create a new part.
Clicking to create a new part actually duplicates that of whatever you had initially selected. Find the duplicate, and adjust the values desired... Part ID, Wall thickness, Part name, Dia etc.
Now, you will need to edit your parts list to imcorporate the part size you just created into the current drawing. It is nested in your toolspace settings tab under pipe network.