Ok, so here's my dilemma. I have a home built in the 60's. The plumbing is all galvanized steel for water lines and drain lines. I recently started updating my bathroom and we have always had problems with the sink draining very slowly.

Recently I became aware
That the galvanized steel tends to corrode quickly causing clogs. Therefore, I would like to replace at least some of the pipe with PVC. However, I am unsure of the process of this. THe sink drain has a fulll piece of pipe about 6-8 feet or so which goes from the horizontal drain pipe heading into the toilet stack to
A fitting for the p trap then continues I would assume to the roof. What is the easiest way of replacing this pipe. Is cutting the answer? And if so, do I need to be worried about the weight of the pipe overhead that continues to the roof, or is this pipe securely fastened to something? Any help would be appreciated

In a day or so, I believe you can post pictures. Use "go advanced/manage attachments" to do so.

Yep, you do need to worry about the weight of the pipe. Removing shingles and replacing the boot is also temperamental.

Are you planning to replace the toilet and it's associated plumbing?

Fernco couplings are the easiest way to join to a galvanized stub.

Do you have a cast iron main drain?

Yes I do have a cast iron main drain . I do plan on replacing the toilet but am reluctant to replace all the other pipe, although I know its what would be best. As of right now, I am mostly concerned with the sink drain pipe.

Could you explain a little more about the Fernco Couplings... unfamiliar with them

Thanks

It's a banded rubber coupling. Fernco Proflex Shielded Plumbing Flexible Coupling, fernco, fernco coupling, fernco couplings, fernco fitting, Shielded Drain Pipe Coupling, Shielded Waste Pipe Coupling, Shielded Vent Pipe Coupling, Flexible Shielded Plumbing Coupling | Fernco (http://www.fernco.com/plumbing/shielded-couplings/proflex-couplings)

They are available at Home Depot.

These basically provide a transition connector between say PVC and galvanized.


Here is another use. http://www.ehow.com/how_4968998_connect-pvc-drains-castiron-pipe.html

I think they mean in the page to support the PVC so the coupling doesn't deform.

If your sink drains directly into the cast iron, Tom has some better ideas.

Removing the galvanized pipe via the threads isn't going to happen easily

Is there a lead/oakum joint that you will be tying into?

As of right now, I am mostly concerned with the sink drain pipe. Could you explain aFerncoCouplings... unfamiliar with them

If this were my call I'd cut the galvanized off at the stack leaving a few inches of the old galvanized to attach a Shielded Coupling, see image) to.
You may then transition to PVC and complete the drain and trap. Since you won't be cutting into the stack to do this I wouldn't worry about it falling down. Good luck, Tom