I own a house that's about 50 years old. Recently, I had a clogged sink and needed a plumber to snake it out. Afterward, I asked him what had caused the clog and he said "nothing - I see a lot of this with the older gavanized pipes." Is that true - that old galvanized pipes "cause" drains to plug up, and if so, should I replace them?

If you have just water going through the pipes and not hair, facial creams, soap residue, etc. galvanized pipes do not "cause" plugged pipes. Hair, facial creams, etc are the culprits of clogged pipes regardless if they are PVC or galvanized.

You may want to undue a section of this galvanized pipe and actually see if these pipes are rusted on the inside. The rusted insides of the pipes can catch the hair, etc. The pipes do not need replaced. They need replaced only if they are leaking.

You may want to ask a trusted plumber about the galvanized pipes causing clogs. If he's honest he'll say the same things I did.

Galvanized pipes have higher internal friction. They catch things.

Keep grease out of your pipes.

Hair is difficult.

Laundry lint is also bad.