We are planning to purchase a classic 2-story house built in 1925 that is entirely galvanized plumbing. A home inspection confirmed that there is poor water flow in the two upstairs bathrooms, downstairs 1/2 bath, kitchen & basement sinks, and outside spigots. There are also
many compression patches in use.

Can somebody give me an overview/understanding of how a house is re-plumbed? And estimated costs? Are new pipes run up from the basement? The house is of such vintage that there are plaster - not sheet rock - walls which might be another consideration on costs. We are planning to have the work done by a licensed plumber, so it's up to code.

Any help would be welcome.