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Old 03-10-2010, 03:08 PM   #1
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Locating Waste Pipe Under Concrete Slab


In the next couple of months I will be constructing a modest addition to my home which will include a half bath. The half bath will be on the main floor of the home, above a finished basement. The architect is just about done with the plans and we haven't yet figured out the best way to tie in the waste drains from the future half bath to the existing plumbing. There are only really two options.

First, we can run the drain line along the basement ceiling in a soffit and tie in with the home's main soil stack. This is the easiest approach, but it creates yet another soffit in the finished basement and it would take some doing to work it around our furnace to the soil stack.

The second option is to tie in underneath the slab. The finished product would be much cleaner and less hobled together and would be my preference, I just need to locate the pipe under the slab.

I think I have a couple of things going for me that might make this easier. 1) This is an older home (75 years old), so I am certain that the waste line is cast iron. 2) The house really isn't that large, so I have a pretty good idea of the route that the 3" line from the basement full bath takes to tie into the main line. 3) The basement full bath is located on the other side of the addition, so we're not far from a drain line. It is certainly possible to tie in and I know the line is somewhere nearby, but I'd rather not go on a treasure hunt to find it. Also, depending on the way it's routed, I might still opt to run the new drain line along the ceiling, depending on how much damage I would need to do to the finished floors in the basement. Some areas are tiled, others have laminate that I could remove and then reinstall, so it depends.

So, my question is, what is the best way to trace a waste line under a concrete slab? I know I can hire a plumber to come and trace the lines, either with a camera or a little beacon, but can this be done DIY? Specifically, can I use a metal detector to find/trace the line? I figure the drain line has to be 6"-12" below the surface, right? 4"-6" slab, maybe more, and then some dirt. Any thoughts about using a metal detector, like those sold at Radio Shack? Has anyone ever done this before? Any other options or methods?

Has anyone ever used one of these pipe locators? Seems hokey to me, but the reviews, on the linked site and elsewhere, are mixed, leaning towards positive. Any experiences?

Any thoughts, suggestions, methods, etc. would be very much appreciated!

Thanks!

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Old 03-10-2010, 03:39 PM   #2
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Locating Waste Pipe Under Concrete Slab


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Specifically, can I use a metal detector to find/trace the line? I figure the drain line has to be 6"-12" below the surface, right? 4"-6" slab, maybe more, and then some dirt. Any thoughts about using a metal detector, like those sold at Radio Shack? Has anyone ever done this before? Any other options or methods?
if the pipe is iron, it is a good chance you could use a good metal detector. If it isn't, you can run a metal fish tape or snake into the pipe and track that but that takes an even better metal detector. If you have a friend with a metal detector, it would be best to try this without buying your own. I have had some good and some bad luck using a metal detector depending on the equipment and the variable involved.



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Has anyone ever used one of these pipe locators? Seems hokey to me, but the reviews, on the linked site and elsewhere, are mixed, leaning towards positive. Any experiences?
a dousing rod. Never had much faith in dousing. I have a friend that swears by it and claimed to be really good at it until I asked him to find a line for me and he was waaaaayyyy off.

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Old 03-10-2010, 05:58 PM   #3
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Locating Waste Pipe Under Concrete Slab


Thanks so much, nice to know it is even remotely possible. Pipe is definitely 3" cast iron, so hopefully I will be in good shape. What constitutes a "good" metal detector? Any recommendations?

Thanks!
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Old 03-10-2010, 07:20 PM   #4
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Locating Waste Pipe Under Concrete Slab


Run hot water down known drain and look for pipe with infared hand held thermometer
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Old 03-10-2010, 08:04 PM   #5
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Locating Waste Pipe Under Concrete Slab


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Run hot water down known drain and look for pipe with infared hand held thermometer
not a bad idea. Since I am an electrician, we usually don't run water down our pipes so I hadn't even thought of that.
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Old 03-10-2010, 09:33 PM   #6
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Locating Waste Pipe Under Concrete Slab


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I figure the drain line has to be 6"-12" below the surface, right? 4"-6" slab, maybe more, and then some dirt. A
hopefully, but not necessarily. It could be quit a bit deeper than that.


P.S. GREAT IDEA above on the infared, but i'm not completely sold that you would transfer enough heat from the water by the time it reached the end. It would be interesting to give it a shot.
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Old 03-10-2010, 09:55 PM   #7
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Locating Waste Pipe Under Concrete Slab


The infrared thermometer sounds like an excellent idea. Some amount of the heat should transfer.

Alan, I am pretty sure it is not all that deep. I've pulled the toilet before and it doesn't go that deep.

Anyway, seems to be worth a shot at least. I might pickup a thermometer from Harbor Freight just to give it a shot. They've got a good return policy.

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