Hi Mike, thanks for attaching the example file.

So I took your curves for the outer surface and joined the elliptical looking pieces together so that there were 6 curves with 2 closed ones (see attached 3DM file). Those curves are all already all nice and smooth with each other (they may have been cut up pieces of one original curve to start with?) so without needing to any other editing other than that joining, you can then build a Network through that whole thing at once, giving this result here:



Looking at that from the underside:



And now compare that to the same outer surface shape in your original model that you did as 4 separate networks rather than all at once:



So that's a pretty good example right there of how to avoid that kind of crease lines appearing between panels - it's generally easier to make things smooth when you build the piece you want to have smooth as all one big surface more like this...

Hope this helps! Sink forms can pretty difficult models to handle where they kind of thicken and change shape in the back part.

- Michael