sitz baths are a basin that fits into a toilet seat (commode?).  They are
designed so overflow of water go into toilet.  Filled with comfortably warm
water.  Mom sits down and eases perineum into water.  Warm water is
soothing.  More water can be added to basin with a bag and tubing that sort
of circulates the water around, overflow going into toilet.  They are rec
in US 3-4 x a day in early postpartum period  for edema, bruising, healing,
pain  control.  You probably use same thing in UK with a different name.
Sorry discription sounds so convoluted.
work - up: this is an American medical term used to describe the process of
looking into every possible cause of a problem.
ie: newborn with fever.  Work - up would include CBC with differential,
cultures.  Hope this helps.  Sincerely, Pat in SNJ