This adapter is attached to an outdoor spigot:

Spigot with adapter

It is near the location of a former hot tub so I believe it has something to do with pressure control. When I attach a hose to it and turn it on if the hose is not flowing (e.g. a closed nozzle at the end) the water leaks (more like squirts, lots of it) from this adapter, it appears to be from the holes and not the connection to the spigot or the hose.

What is this thing? Is there a way to utilize it? I'd like to remove it so I can use this spigot but when I try to unscrew it with a wrench it does not budge - in fact the spigot itself starts to rotate. I wasn't really able to tighten a pipe wrench to the spigot due to the available clearance & pipe width.

There appears to be a rivot on the under side of the adapter but it is difficult to tell, it is somewhat rusted over.

Follow Up

My original concern was water leaking from it when it was used. While a plumber was on site doing a different job I asked him to look at this to see if something was wrong. He said the vacuum breaker wasn't working properly and ended up replacing the entire hose bib (with new vacuum breaker), I presume because he was not able to remove the vacuum breaker as well or it wasn't salvageable. Now no water spews out when it is used.

  • 1
    It looks like a anti syphon device to me, because of the petina on the faucet I'd different than the device I would guess it is aftermarket. The "rivet" may be a rusty screw to keep it from coming off. – Ed Beal Jul 22 '17 at 15:09
  • You might be able to grip the spigot body with a pipe wrench if you first remove the handle, packing nut, and stem. (If you remove only the handle, you are likely to bend or break the stem.) – A. I. Breveleri Jul 22 '17 at 15:15
  • Sometimes the anti-siphon device is not an add-on, yet will still have the set-screw commonly found on after-market ones. Look carefully, sometimes the portion of the device that threads onto the hose valve is actually crimped on there to prevent removal. If this is the case, you would have to replace the whole valve. – Jimmy Fix-it Jul 22 '17 at 16:34
  • Is this a continuous flow of water for as long as the nozzle valve is closed, or is it a brief spurt and then the flow onto the ground shuts down? – ThreePhaseEel Jul 23 '17 at 0:06
  • You should be able to put an adjustable "crescent" wrench on the sides of the body of the spigot, without taking it apart. – DaveM Jul 24 '17 at 3:18

An anti-siphon plumbing device is a special device that has a one-way valve designed to stop the flow of potentially contaminated water back into the drinkable (potable) water supply.

Anti-siphoning capabilities are required by code on certain plumbing devices such as exterior faucets (sillcocks).

On exterior faucets or sill-cocks, the anti-siphon device protects against the risk of the faucet being connected to a hose that is immersed in contaminated water or attached to a chemical sprayer.

These special faucets keep freezing cold temperatures away from any water supply line feeding the exterior faucet. They allow remote control of the water supply faucet valve located inside the home, which then controls water flow to the exterior faucet spout. The faucet head is attached to a 6” to 20” long tube.


I agree that this appears to be an add-on device which could probably be removed with a locking pliers or pipe wrench.


This is defiantly an add on vacuum breaker. As mentioned in @isherwood's answer it is a form of anti-siphon device.

enter image description here

The device simply screws over the existing hose bib connection, adds a simple vacuum breaker, and a new hose connection on it's end. Unless it is broken, there should be no need to remove it.

Most are held in place via a set screw. This is most likely the ‘rivet’ you observed. The set screw might be might have a round head, hex head, or even a hex key. Some are designed to that you break the head of the screw off after install so that it remains permanent. Most newer codes require that hose bibs be of the anti-siphon type and this devise is often used when upgrading an existing hose bib to meet code.


This might be normal. Really!

The device you're talking about is a hose bibb vacuum breaker that protects the water system from backsiphonage. Without it, leaving your hose end in the backyard kiddie pool could turn into a real mess for you and the City if a water pipe breaks or needs to be turned off for maintenance at the wrong time.

Closing the valve on the hose nozzle creates a situation similar to backpressure, as the pressure change from the nozzle closing propagates back up the hose and pipe past the vacuum breaker. The vacuum breaker is spitting out water to keep that water from getting into your plumbing because it might not be just water -- it might have crud in it that you don't want in your plumbing.

If it spits out water all the time not just in a burst when the valve is closed though, it might be faulty or jammed inside. I'd replace it with a new one though, or if you're willing to do some plumbing, replace the whole hose bibb with a frost-free type that has an integral vacuum breaker.

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