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I'm deciding whether to repair or replace my ancient cast iron DWV plumbing while the walls and ceilings are open.

The 1.5" steel shower/tub drain is currently notched through joists for a run of about five feet, incorporating a long trap, through three joists. I neither want to drill more holes in the joists nor use a drop ceiling, nor remove the beautiful marble floor above. The replacement will be in place.

My question concerns threading 1.5" PVC through the existing holes: I'm assuming I'll have to assemble from sections. Is it terrible to introduce couplings to a PVC drain, or is this very common and I shouldn't worry?

Would there be any benefit to using copper? Or some other material?

I might prefer to keep the steel if rodding would get it all the way clean--it's close to solid crud inside--any relevant experiences helpful here.

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    It's almost unheard of for well-prepared PVC connections to fail. The cement essentially welds the parts together, and there's virtually no pressure in the system. – isherwood Jan 28 '18 at 0:37
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Coupling a drain through the joists are even done in new work, sometimes it is the only way.

Cast iron and especially any galvanized pipe connected to it will sure rust through over the ages. If you have any galvanized pipe in place and you yank on it a bit, you may find it readily cracks loose or separates at the joints. If the cast iron is in good shape, many times the shaking of the pipes during renovation will cause the leaded joints to leak.

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