I have a 35 year old house with copper pipes. Our water has a good bit
of iron and for a long time the people who lived here before us did not
have a water softener. I've opened the lines a few times for various
repairs and find what I believe is buildup of iron. When it's wet it
looks and feels a bit like rusty colored seaweed built up on the walls
of the pipe. Once it dries it turns to very fine rusty powder, about
the consistency of talcum powder, and is easily wiped out or blown
away.

I have normal range at the pressure tank (45-60psi) and good flow rate
at the base of the pressure tank, but many fixtures in the house,
especially the outdoor faucets, have low flow rate.

My question is how can I remove this iron deposit, or whatever it is,
from the inside of the pipes. I've googled this a little and have not
found a description that quite matches what I see inside my pipes.
There are many articles on mineral buildup, crystalline materials, and
all kinds of hard deposits. But my deposits are very soft and easy to
remove. Could I, for example, drain down the whole house piping system,
blow compressed air through the lines starting at the top of the house
to dry out all the lines and then turn the water back on to flush out
the powder? Would this work or would the pipes stay too damp for the
rust to turn into powder?

Any suggestions welcome.