Want to cull pics, delete them from darktable AND from my HDD, including the sidekick file.
Making a bit of a mess of it at the moment by deleting RAWs in Faststone Image Viewer and then the sidekick file in file manager, there has to be an wasier way!! 
From the manual:
Select in lighttable, then in right sidebar: “Actions on selection” → “delete (trash)”.
As usual, test on a small sample.
Thanks rvietor, I should have checked the manual!
I actually cull my pictures in darkroom mode when editing in DT by using the keyboard shortcut of r for reject. Then later in lightroom view I filter for rejected only images and do as Rivietor suggests and delete them which gets rid of the side car file as well. That normally sends to to the trash on my windows computer and I can still recover them until I clear my trash. Deleting them outside of DT is a pain in the butt because you end up with skulls everywhere.