Drain, waste and vent piping is a different set of materials from supply, chosen for different reasons.
PVC
White rigid plastic, solvent-welded with primer and cement.
Advantages: inexpensive, light, easy to cut and join, widely available, and resistant to most household chemicals.
Disadvantages: noisy — water falling down a stack is audible through a wall; it expands and contracts with temperature, which matters on long runs; and it needs support at closer intervals than metal.
The most common DWV material in new residential construction across much of the US.
ABS
Black rigid plastic, joined with a one-step cement and no primer.
Advantages: the same as PVC, plus slightly better impact resistance at low temperature and a simpler joining process.
Disadvantages: the same noise, and it degrades under ultraviolet if left exposed.
PVC and ABS are not interchangeable and must not be solvent-welded to each other. Transition cement exists and is not accepted everywhere; a mechanical coupling is the reliable answer. Which of the two is permitted varies by jurisdiction, and some allow only one.
Cast iron
Heavy, joined historically with lead and oakum and now with rubber couplings and stainless clamps — no-hub or hubless systems.
Advantages: very quiet, which is why it is still specified for stacks in walls adjoining living space and in multi-family construction; fire resistance; and a very long life where it is not exposed to aggressive conditions.
Disadvantages: expensive; heavy enough to need proper support and two people; and it corrodes over decades, particularly at the invert where it carries waste.
Old materials still in houses
Galvanised steel drains, used before the 1960s. They corrode internally and narrow progressively, and by now most are substantially restricted. Slow drains throughout an old house are frequently this.
Clay, for the building sewer. Root-prone at every joint and brittle.
Orangeburg, bituminous fibre, from the 1940s to the 1970s. It deforms and collapses, and it has a short life. A house of that era with an original sewer line should be inspected.
Lead bends under old fixtures, which are usually replaced when the bathroom is opened.
Mixing materials
Transitions between plastic and cast iron use a rubber coupling with a stainless shield — a no-hub coupling — which is the standard fitting and is accepted everywhere.
Rubber "Fernco" couplings without a shield are for repair and are not permitted in every location, particularly where they would be buried or inaccessible.
Noise
This is the practical difference people notice.
A PVC stack behind a bedroom wall carries every flush audibly. The remedies: cast iron for that section, wrapping the stack in a mass-loaded barrier, or filling the stud bay with insulation — which helps and does less than the pipe material does.
On a new build, specifying cast iron for the stack in a wall adjoining a bedroom is a small extra cost and the kind of decision that is impossible to revisit later.
Support and expansion
Plastic needs support at closer intervals than metal — the code specifies the spacing — and it sags between hangers over time, creating the low spots that catch solids.
On long horizontal runs, expansion has to be allowed for, or the pipe bows between fixed points and the fall changes.
Fittings are material-specific
DWV fittings come in the same materials and they are directional — long-sweep bends, wyes, combination wyes, sanitary tees each with a defined use.
Pressure fittings from the supply side look similar in plastic and are not interchangeable: they have sharp internal shoulders that catch solids, and they are not rated for the same joining method.
Buying a fitting because it is the right diameter and the right colour is one of the more common DIY errors, and the consequence is a drain that blocks at that point for the life of the house.
Testing before closing up
New DWV work is tested before the walls close — typically filled with water to a stated head and observed, or air-tested.
That test is part of the rough-in inspection, and it is the only opportunity to find a joint that was not properly cemented. A leak found then is a fitting; the same leak found later is a ceiling.