To exhaust through heavy labour.
run someone ragged
To exhaust; to demand excessive effort or work from somebody.
grunt work
Work (especially that which is heavy, repetitive or mindless) that is …
heavy lifting
The most demanding part of an endeavour; work requiring the most effor…
work one's magic
To achieve something favourable and desired through the application of…
puzzle through
To work methodically to solve or understand something complex.
prepare the ground
To carry out any preliminary work that will enable something to occur.