In medicine if you want to know about the flow of food through the intestinal tract you feed the patient a Barium Meal and X-ray them.

Is there any way to achieve a similar sort of result in domestic pipework? I have a blockage in some drains and I have access to most of the pipework, but I can't immediately tell WHERE the blockage is.

It would be lovely if I could get out by trusty X-Ray scanner app on my iPhone and just look inside the pipes ... but that doesn't exist.

Is there any way that I can (on a DIY budget) detect / trace the flow of water from the plug hole to the main sewer entrance.

Majority of the pipes in question are plastic, if that's relevant.

  • Title edited for clarity among non-medical types. Normally, there are enough branches and fixtures in plumbing system so that the approximate location of an obstruction is apparent. Is that not the case for you? – isherwood May 17 '16 at 17:09

The following two techniques are perhaps not the best methods, but they're basically free, and don't require any tools. Pinpointing the blockage might not be realistic, and practice may be helpful. Using both techniqes might help get you within a foot of the obstruction.

If the pipe is partially blocked (such that it will drain after a couple hours) the best no-tool method to use is your forearm. After the drain has... drained, fill the partially-blocked pipe with hot water, and feel the pipe with your forearm (which is pretty sensitive to temperature). An infrared camera would be a cool tool for this, or a temperature gun might be just as good, but they aren't commonly owned tools, and your forearm will probably work.

If the pipe is really blocked (and full of water such that adding hot water would not work), then you might be able to tap on it with a screw driver and hear the empty versus dense/full sound. The sound of a full pipe is a little unusual, and the difference between full and empty is subtle, but it's still possible to hear.

  • Great, practical ideas! – Brondahl May 18 '16 at 11:01
  • FYI ... this worked like a charm... I now know exactly where the blockage is. – Brondahl May 19 '16 at 10:51
  • @Brondahl glad to hear that. – Ben Welborn May 19 '16 at 12:21

Call a pro

Call Roto-Rooter®, or any other plumber of your choice. They'll be able to feed a camera down the line, and tell you exactly where, and what the clog is. Even without a fancy camera, a plumber should be able to use a regular snake to locate the clog.

Use a snake

If you want to give it a try yourself, plumbing snakes (auger) are available at any hardware or home improvement store. They're available from many different manufacturers, in both hand powered, drill powered, and motor powered depending on your budget.

Using a snake is easy, but it takes a bit of practice to get a feel for locating clogs. Keep track of how much line you have fed out, and make note of it when you hit the clog. Then measure along the pipe, to determine the location of the clog.


If the pipes are all plastic (PVC, ABS, etc.), a strong magnet might help.

  • Get a strong magnet with a hole in it.
  • Tie a string to the magnet.
  • Put the magnet in the drain, and use a large volume of water to flush it down the drain.
  • Run another strong magnet along the outside of the pipe, until you feel the magnet inside the pipe.

Flushable transmitters

Flushable transmitters are available, that can be sent down the drain line. Once in the line, the transmitter can be located using a receiver.

Credit to @Ed Beal


If the pipe is large enough, or you can find a robotic ball small enough (Sphero for example). You could send the robot down the drain to locate the clog. Getting the robot back, might be a challenge.


  • Anything you put down the drain will have to be retrieved, or small enough to be processed by the waste treatment center.
  • Anything put down the drain should not be damaging to the drain system, nor the sewage system.
  • I like the magnet idea I have never done that I usually run a snake down. – Ed Beal May 17 '16 at 18:30
  • @EdBeal not sure if it will work. The magnet has to be light enough that water can move it, but strong enough to reach through the pipe wall. – Tester101 May 17 '16 at 18:45
  • 1
    they do make a plumbing ball that is a radio transmitter. I thought that was sphero until I looked at it. some rental places carry the units mostly for finding main drain lines. The balls only transmit for a few hours and they go into the tank or main sewer line. I think the balls were 20$ and the receiver rental was 20 but that was back in 2002 I had a house that we could not find the septic tank (was not where the plot plan showed). Flushed the ball and found the tank almost 100' west of the location it was supposed to be put. not sure why they did it that way as the yard was flat . – Ed Beal May 17 '16 at 19:11
  • You can rent a drain camera at many equipment rental places if you really want to do it yourself. But I'd just call a pro since after he finds the blockage, he'll have the right equipment to clear it (and he's the one that has to clean up his equipment after pulling it out of your sewer line) – Johnny May 17 '16 at 20:30
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    Really interesting and clever ways to do this, but ultimately I think that Ben's ideas are the ones that I'm going to actually use tonight, so I'm accepting his answer (but upvoting them both). Sorry! – Brondahl May 18 '16 at 11:00

If you can't access the pipe to check temperature as suggested above, you can estimate by volume. 10 feet of 1.5" pipe holds .92 gallons of water. So if the blockage has completely drained overnight and there's just a little water in the trap, and then it takes a gallon to full the pipe back up, you know the blockage is a little over 10 feet down (so a 25' auger has a chance to work).

  • Good line of thinking -- keep the answers coming! – ThreePhaseEel Jan 26 '19 at 0:29

The other answers are great, however can I add good old detective work using process of elimination and our friends trial and error.

If it is only two drains, locate where they link together and do your best to hit that spot with a snake. If its every drain well hire someone to look at the main stack water flows down hill.

Final thought maybe its not one single blockage but multiple little blockages.

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