Those solar showers do work well, been using one in Baja for years.  Most
boating supply cats have em.  They are a bit cheezy and tend to be good for
only a few months of continuous use.  The valves go bad if you don't
puncture the bag first.  We always take along a spare to Baja.  They roll up
nice and take little room.  Good for two people to clean up, if you are in
Baja..(there are relative degrees of cleanliness, si?)  If you need to get
it just a little more hot due to an extended "beer-thirty" or the sun goes
behind a cloud,  my gal heats up a pan of water and pour that into the bag..
  One less think to keep running, those solar showers.  And, they add
freshwater capacity to your out-back travels.  We water the dogs from ours
sometimes..
  Of course, most don't leave civilization for weeks..
  Good enough, the plain cheap solar showers.
  Don Hanson