Kevin wrote:
I'm still not quite getting the diverters though. The only thing that
seems to make sense is if the inputs contribute to the number of ways,
so a 3-way diverter has one input and two outputs and the 5-way has two
inputs and three outputs. Though I don't really understand why you
would need two inputs unless you were using it as a mixer too. Also it
doesn't really explain why Chris would have to change from a 3 to a
5-way in the middle of the job.

A three way diverter gives you A, A+B or B.

At a guess, a five way diverter gives you A, A+B, B, B+ C, C.

Better than using a divertor valve is to use something like the
DE2000RC on this page:

http://www.avalon-bathrooms.co.uk/ac...Showers.htm l

Which is a dual "volume control" rather than a diverter, this gives you
analogue control over how much water comes through each outlet from
none to full-on, rather than just on/off and whatever the resistances
in the plumbing 'decide' is the right proportion to send each way.
That one has the thermostatic valve built in as well, which makes the
plumbing simpler, but I'm sure you can them without if you prefer.