By “dip” I mean a sag in the drainpipe below its normal (designed) frainage slope. This happens when a run of drainpipe sags in the middle of a run. You can see that in crawspaces and basements with poorly supported pipe runs. You also can find it in buried runs of soil pipe, for example where a “sink spot” develops under the buried run.
Such buried sags cannot be corrected by trenchless sewering, since the new pipe is simply pulled through the buried pipe, and the PE pipe is somewhat flexible (i.e. it will follow the sag).
That being said, if the pipe slope is good, trenchless sewering can be a less expensive way to replace a long run of buried sewer line. The main costs of sewer replacement are: 1) labor; and 2) materials. On both counts, trenching out an old line and replacing it with hubless CIP and fittings is more expensive than doing a trenchless job with PE pipe, unless you have a really short run to replace.
I stopped doing major residential sewer line replumbs several years ago because of the time and labor (backbreaking) involved, and the fact that we have several trenchless sewer tapping outfits here.
I can’t say anything about your local costs, but in the SF Bay Area, replacing a 60′ run of sewer line would run the homeowner about $10-12K by “conventional” means, and $6-7K trenchless. So figure on a 30-40% savings…