Following the steps:
Fill - Fills sinks in a surface raster to remove small imperfections in the data.
Flow Direction - Creates a raster of flow direction from each cell to its steepest downslope neighbor.
Flow Accumulation - Creates a raster of accumulated flow into each cell. A weight factor can optionally be applied.
Corrected the mistakes of the DTM , need to extract the drainage network
Not an answer but a comment. The steps are pretty much the same as described here for ArcMap
https://support.esri.com/en/technical-article/000011289. It would seem as if FME has transformers for the last two steps but there does not seem to be one for flow direction and flow accumulation. Surely someone must have solved this by now?
Not a full solution yet but a step along the way
I'm taking a DEM and turning it into polygons. For each polygon I generate a line connecting it to it's lowest neighbor.