PVC Adapters and Bushings

An adapter or bushing is the part that gets two things to meet that won’t on their own: PVC pipe to a threaded valve, a 1-1/2-inch branch into a 2-inch drain, a sink trap onto the drain line. The whole trick is knowing what each end of the fitting is. Read the ends right, and you’ll walk out with the right part the first time.

Read the ends

Every adapter and bushing is named by its two ends.

Code	What it is	What it connects to
Slip, SOLV, socket, hub	A cup the pipe glues into	The outside of PVC pipe
Spigot, SPG	Sized like the outside of the pipe	Glues into another fitting’s socket, not into pipe
MPT, MIP	Male pipe threads on the outside	A female threaded fitting, valve or tank
FPT, FIP	Female pipe threads on the inside	A male threaded nipple, valve or plug

So a “1-1/2 slip x 1-1/2 MIP adapter” glues onto 1-1/2-inch pipe and gives you male threads. A “2 spigot x 1-1/2 FPT bushing” glues into a 2-inch fitting and gives you 1-1/2-inch female threads.

The one people get wrong: a spigot end won’t go into pipe. It goes into a fitting.

Going from glued pipe to threads: male and female adapters

This is the most common reason people need an adapter: getting PVC pipe onto something threaded, like a valve, a pump, a pressure tank, a hose bibb or a sprinkler line.

• Male adapters (slip x MIP) give you outside threads. WBC carries them from 1/2 to 2 inches, including reducing ones (1/2 x 3/4, 3/4 x 1/2, 1 x 3/4), and hub x MIP for drain lines.
• Female adapters (slip x FIP) give you inside threads, 1/2 to 2 inches, plus a 3/4 x 1/2 reducing one. The DWV female adapters (hub x FPT) in 1-1/2, 2, 3 and 4 inch take a threaded plug or connection on a drain line.

On the threads: seal the male threads the way the fitting’s maker says, usually PTFE tape or a thread sealant made for plastic; some pipe dopes attack PVC. Thread it snug, not cranked. Overtightened plastic threads crack, and the leak shows up later.

Reducing a size: bushings

A bushing reduces a size inside a fitting, and it’s shorter than a reducing coupling. That’s handy in a tight spot.

• Spigot x slip bushings glue into a larger fitting and take smaller pipe: 3/4 x 1/2 up to 2 x 1-1/2.
• Spigot x FPT bushings glue into a larger fitting and give you a smaller female thread, from 3/4 x 1/2 up to 2 x 1-1/2. That’s how you put a threaded valve or gauge onto a bigger line.
• Threaded bushings (MPT x FPT) step down a threaded connection: 3/4 x 1/2 up to 2 x 1-1/2.
• DWV flush bushings (spigot x hub) let a smaller drain branch into a larger fitting: 2 x 1-1/2, 3 x 2, 4 x 2 and 4 x 3. A 4 x 2 brings a 2-inch branch into a 4-inch fitting. Drains get bigger as they go, never smaller: water flows from the small pipe into the big one.

Sink drains: trap adapters

A trap adapter is where the sink’s trap meets the drain pipe in the wall. One end glues to the drain fitting or pipe; the other has a slip nut and washer that tighten around the trap arm, the horizontal piece coming off the trap, so you can take it apart later.

• 1-1/2 inch is the usual kitchen sink size.
• 1-1/2 x 1-1/4 puts a 1-1/4-inch bathroom sink trap onto a 1-1/2-inch drain.
• Check the glue end: some trap adapters glue into a fitting’s hub, others take pipe into their own socket. Look at what’s coming out of the wall and match it.

WBC carries trap adapters in 1-1/4, 1-1/2 and 1-1/2 x 1-1/4, male and female.

Changing pipe types: the 4-inch transitions

Schedule 40 DWV pipe and the thinner sewer-and-drain (S&D) pipe used underground aren’t the same outside size, so they don’t glue together directly. A 4-inch Schedule 40 hub x sewer-and-drain bushing makes that change, typically where the house drain heads outside toward the septic or sewer. That kind of fitting is for drainage that isn’t under pressure.

The 4-inch hub x hub coupling adapter joins two 4-inch pipes end to end. Check the label for which pipe each hub takes, and match it to what you’ve got.

What these fittings are for, and not for

• Drain fittings (DWV) are for drains. They’re not made for water under pressure. For water lines, use fittings rated for pressure, and check the maker’s rating; “Schedule 40” on its own doesn’t tell you the pressure rating.
• Cold water only. PVC is rated to 140°F. It’s not for hot water lines.
• Never compressed air. PVC fittings aren’t for compressed air or gas, and that includes pressure-testing with air.
• Glue right: clean, primer, then PVC cement, and let it cure the time on the can before you put pressure on it.

In a Montana well house or a buried stock-tank line, these are the parts that get PVC onto a threaded valve or pump fitting. Keep anything with water in it below the frost line or drained for winter.

The Pick

To put PVC onto something threaded, a slip x MIP or slip x FIP adapter in your pipe size. To step down a size inside a fitting, a spigot bushing. To hook up a sink, a trap adapter, 1-1/2 for the kitchen or 1-1/2 x 1-1/4 for the bathroom. To go from house drain to underground sewer pipe, the 4-inch Schedule 40 x sewer-and-drain bushing.

Frequently Asked Questions

What’s the difference between an adapter and a bushing?

An adapter changes the kind of connection, like glued pipe to threads. A bushing reduces a size and fits inside a larger fitting.

What does spigot mean on a PVC fitting?

A spigot end is sized like the outside of the pipe, so it glues into another fitting’s socket. It won’t go into pipe.

What size trap adapter for a bathroom sink?

Usually 1-1/2 x 1-1/4: a 1-1/4-inch trap onto a 1-1/2-inch drain. Kitchen sinks usually use 1-1/2.

Do I use Teflon tape on PVC threads?

Usually, on the male threads, or use a thread sealant made for plastic. Follow the fitting maker’s instructions, and don’t overtighten.

Can I use DWV fittings for water lines?

No. DWV fittings are for drains that aren’t under pressure. Use pressure-rated fittings for water lines.