This Old Recap

Field guide

PEX, copper, and cast iron: which pipe, which joint, and when

A homeowner opening a wall finds PEX, copper and cast iron and has to decide what connects to what; the guide sorts them by the job, from the episodes.

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8 min read

Open a wall in an older house and you can find three plumbing eras at once: copper supply lines, PEX snaking through the joists, and a cast-iron drain stack dropping to the basement. Each one is right for the job it was put there for, and each one connects differently. This guide sorts them by the job, from the episodes: which pipe carries water in, which pipe carries it away, and which joint belongs where — plus the small parts, a frost-proof spigot, a toilet flange, and an anode rod, that decide whether the system quietly works or quietly leaks.

Supply and drain are two different systems

The first sort is the one the episodes keep coming back to: supply lines and drain lines are not the same job, and the materials do not cross over. PEX and copper carry pressurised water in. Cast iron and PVC carry waste water out, by gravity. A push-to-connect tee can join PEX to copper on the supply side; nothing in these episodes joins a supply line to a drain. When a segment talks about a joint, it is always inside one system or the other.

The second sort is who does the work. The recaps grade each job, and the grades are consistent: small supply jobs are DIY-able with care, while drain and sewer work is trade work. The scale runs through the guide below — a 5 out of 10 for the outdoor spigot, a moderate grade for the flange, a 7 for the anode rod with a backup plan, and 2 out of 10 for cast-iron drainage and sewer work, which is the show's way of saying call a plumber.

PEX vs copper: the debate

Season 23, Episode 21 is the one place the show stages the PEX-vs-copper argument directly, and neither side wins outright. Copper is time-proven and rigid: it runs in straight, logical lines through a building, it resists corrosion, and modern solder contains no lead. That rigidity is the point where a valve needs securing — around a shower valve, for example — and it is why remodels tie into existing copper rather than starting over. Copper is also the established choice in northern urban areas, where the housing stock is already copper.

PEX — cross-linked polyethylene — is flexible, more like wire than pipe. It bends around corners instead of needing a fitting at every turn, and fittings are leak points, so fewer fittings in the walls is a real advantage. The fittings often cost about half what copper fittings cost, and the connections go faster. In the expansion demonstration, a sleeve goes over the tubing, the tool expands it, and the material's memory pulls it tight around the fitting — a solderless joint. The manual expansion tool, Richard notes, now costs about what a torch kit costs and never runs out of gas. His judgment is that properly manufactured PEX should last as long as copper and then some; he gives no number of years, and neither does this guide.

Two limits from the same episode. A whole-house repipe is not a weekend DIY job, whichever material you pick. And the drip-irrigation segment in that episode is a reminder that PEX is not only for inside walls — it also feeds the drip lines in the Austin garden — but that is a side note, not a second debate.

PEX joints: expansion, crimp, or push-to-connect

The outdoor spigot in Season 25, Episode 3 is where the three PEX joints get priced against each other, because the job needs a new line tied into an existing copper one. Push-to-connect needs no tool at all. A PEX-B crimp job — ring or sleeve squeezed onto the fitting — came to about $120 for fittings and tool. PEX-A expansion, Richard's preferred joint, came to about $150 with the tool. Tying into the existing copper with them, as a copper job, would have cost more than $200 in parts. Nick picks PEX-A.

For PEX-A, the choice is between a manual expansion kit (opens in a new tab) and a cordless expansion tool (opens in a new tab). For PEX-B, the crimping tool kit (opens in a new tab) covers the ring-and-tool route in one box. The tie-in itself uses a copper-to-PEX push-to-connect tee (opens in a new tab) — no torch, no solder, no waiting for a joint to cool.

But the episode is blunt about the part that is not a casual Saturday job. Richard's line: "It's not completely do-it-yourself." The water has to be shut off, and a copper supply line has to be cut open. The segment grades it 5 out of 10.

The cutting details matter because push-to-connect fittings seal with O-rings. Clean the copper with emery cloth, mark both sides of the cut, and use a small tubing cutter. No hacksaw: burrs and O-rings do not mix, and a burred end will not seat. Cut the PEX square with a PEX tubing cutter (opens in a new tab) — but both iCrimp kits above already include a cutter, so do not buy this as well. Cut the copper with a close-quarters tubing cutter (opens in a new tab) where a full-size cutter cannot spin between studs, and clean the cut end inside and out with a inner-outer reamer (opens in a new tab) so the joint seats fully.

Copper joints: solder or press

Solder is the copper joint the episodes treat as the default: a torch, flux, and solder, with the pipe cleaned first — the emery cloth from the spigot segment does the same work here. The trigger-start torch kit (opens in a new tab) is the standard trigger-start torch, and MAP-Pro burns hotter than propane, so a 3/4-inch joint comes up to temperature faster. Solder, flux, and brush are bought separately; they are not in the kit.

Press is the flameless alternative: a press tool squeezes a fitting onto the pipe with no flame, which is what you want inside a finished wall where a torch is unwelcome. It is a pro-priced rental tool, not a DIY purchase — see the note in Why these picks below.

The frost-proof sillcock

The spigot in Season 25, Episode 3 is a frost-proof sillcock, and the frost-proof part is not in the handle — it is in the length. The shutoff sits back inside the warm wall, so when the handle is closed the water in the tube drains out instead of sitting outside to freeze. The Woodford Model 19 sillcock (opens in a new tab) is the one in the episode, with a pressure-relief valve that stops the tube bursting if a hose is left on. Measure the wall thickness before ordering: the 19CP-8 is the episode's model, and the 12-inch 19CP-12 is the common pick for thicker walls.

Drains: cast iron where it is quiet, PVC everywhere else

Season 48, Episode 4 runs the new supply lines inside the house — PEX in an outside wall would freeze — and then turns to the drains. Cast iron appears in exactly one place: through the kitchen and family room, where its weight keeps the drain quiet. On this run it cost about three times what PVC would have cost, and that is the figure for this run, not a general price rule. Everywhere else the drain is PVC: "PVC is the standard: easy to glue, lasts forever."

The bench work shows why cast-iron drainage is trade work. The fittings join with mechanical couplings, and the pipe is cut with a in-place soil pipe cutter (opens in a new tab) — "a chain with sharp blades; enough pressure snaps the pipe in a clean cut." The run transitions back to PVC in the basement and ties into the main drain, with a Fernco Proflex 3000-44 (opens in a new tab) shielded coupling at the change of material. The segment grades it 2 out of 10.

One small piece of insurance from the same episode: a $70 steel plate over a concealed toilet tank, where a screw could otherwise find the tank. Cheap protection for a part you cannot see.

The sewer: smaller pipe, better flush

Season 48, Episode 5 goes outside, to the sewer. The original run was 4-inch cast iron inside the house and 6-inch clay outside; the remodel goes 3-inch inside and 4-inch outside. Smaller wins for a low-flow toilet: a 1.28-gallon flush moves well in a 3-inch pipe, slower in a 4-inch, and in the 6-inch it is "just trickling", with paper not coming through. Craig's caveat is that the rest of the house helps — water from sinks and laundry can push a hang-up along — so the small pipe is not carrying the flush alone.

Replacing the old clay run means pipe bursting: about 80 feet of old clay pipe, a 30-ton hydraulic piston pulling the new pipe through about a foot at a time. It is a pro job, graded 2 out of 10, and there is nothing to link to here — no tool in this guide bursts a sewer. The episode cites no code section for the sizing, and this guide adds none: sewer sizing, like permits, varies by jurisdiction, so check the local code before assuming the sizes in this episode apply to your house.

The toilet flange: a small part that stops a big leak

Season 24, Episode 11 is about the closet flange — the PVC, cast-iron, or stainless ring bolted to the floor that anchors the toilet to the framing, not to the pipe. A rocking toilet deforms the wax ring underneath it, and a deformed wax ring leaks sewer gas into the room. The fix depends on how much the floor has been built up since the flange was set. A wax ring with a horn buys about 3/4 of an inch of build-up, and the episode calls that the edge of workable. Higher than that, the choice is flange shims with a conventional wax ring, or a kit with a rubber seal instead of wax and longer bolts, useful for roughly 1 to 1.5 inches.

The limits are structural. A cracked flange, a rotted subfloor, or a cast-iron flange in poor shape is a plumber's job, and no kit repairs rot. The episode grades the flange job as moderate — approachable when the flange and floor are sound, and a stop-and-call-a-pro job when they are not.

The anode rod: the part that rusts so the tank does not

Season 24, Episode 9 opens a water heater to show the anode rod — a rod of aluminum, magnesium, or zinc that corrodes first, sparing the glass-lined steel tank. Replace it every 2 to 5 years, the episode says, and a tank can last twice as long. A new rod costs about $40; a new heater approaches $1,000. That is the whole economics of the job.

Getting the old rod out is the work. The nut is 1 1/16 inches. A breaker bar fails; an impact gun with a six-point socket breaks it free. The old anode comes out as "a wiry skeleton, almost completely consumed" — which is the rod doing its job. While the heater is open, drain a few buckets from the bottom spigot every six months to clear sediment. The segment grades it 7 out of 10 with a backup plan: the risk is damaging the heater, the plumbing, or the gas vent, not injury.

DIY confidence — and when to call a pro

Put the grades together and the pattern is plain. A spigot at 5 out of 10, a flange at moderate, and an anode rod at 7 out of 10 with a backup plan are all DIY-able with care and the right tool for the joint. Cast-iron drainage, the sewer, a whole-house repipe, and anything gas-adjacent sit at 2 out of 10 — trade work, not a learning project.

Two standing cautions. First, code and permits vary by jurisdiction: where a job touches the main line, the sewer, or gas, check the local code and whether a permit or a licensed pro is required before starting. Second, shut the water off before cutting any supply line, and have a plan for the water already in the pipe — the spigot segment's warning, "It's not completely do-it-yourself," is about exactly that moment.

Why these picks

The links above go to the specific products we picked for each job, not to an Amazon search — and where a material or tool comes in different types for different jobs, we set out the options by main use instead of a single pick. Each one is a mid-range, reputable-brand pick for a DIYer — not the cheapest option, and not a pro-only tool. Prices change, so none are quoted here; the link is the current listing.

PEX-A expansion: manual or cordless

PEX-B crimp: one kit

The bridge: push-to-connect

Cutting: PEX, copper, and the burr

Soldering copper: the torch

Press copper: rent, do not buy

  • Milwaukee M18 FORCE LOGIC Press Tool Kit 2922-22 — the flameless joint for a finished wall where a torch is unwelcome, but a pro-priced rental tool, not a DIY purchase. There is no product link for it: the listing shows no featured offers, so there is nothing to buy through it, and buying a press tool for one joint makes no sense in any case.

Cast iron: cut it rented, join it shielded

  • RIDGID 226 In-Place Soil Pipe Cutter (opens in a new tab) — the exact tool type in the drain segment: a chain with sharp blades that snaps cast iron clean, in a short in-place form for cutting against a wall. Rent it for one cut; buying it for one cut makes no sense — this model is available for rent at Home Depot.
  • Fernco Proflex 3000-44 (opens in a new tab) — the shielded coupling for the cast-iron-to-PVC transition in the drain segment; the steel shield keeps the joint rigid. There is no product link for it — no ASIN was found — so it links to a search instead. Match the coupling to your pipe size: the 3000-44 is 4-inch cast iron to 4-inch plastic, and 4-inch is the size in this episode, not a universal size. Do not use the 3001-44 — that is cast iron to copper, the wrong coupling here.

The sillcock

  • Woodford Model 19 Freezeless Anti-Rupture Sillcock 19CP-8 (opens in a new tab) — the frost-proof sillcock from the spigot segment: the shutoff sits back inside the warm wall, and the pressure-relief valve stops the tube bursting if a hose is left on. Measure the wall thickness first — the 12-inch 19CP-12 is the common pick for thicker walls, and no listing was found for it, so it has no link here.

The sewer: no product

There is nothing to link to for the sewer segment — pipe bursting with a 30-ton piston is a pro job, and no tool in this guide does it.

Where this was shown

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