all the water lines inside my home are 1/2 inch, although the outdoor
supply is 3/4
we have a single copper 1/2 inch line servicing the bathroom. it
supplies the toilet sink and finally the shower
if someone flushes the toilet while someone is in the shower they get
the cold water pressure and flow drops nearly all goes to the toilet.
my fix is add a hot and cold PEX lines just for the shower from the
hot water tank area.
i think this would decrease the problem a lot.
my neighbor thinks it wouldnt help. he will be helping snake the line
and feels the pex is a waste of time.