I tagged this question to an older thread, but I fear it may have gotten lost.

I am trying to locate my existing 3" cast iron waste line under my concrete basement slab. I know that I can bring in a pro to run a camera or a locator beacon, but I would like to try this on my own, if remotely feasible. I've got a pretty good idea of where it runs, the home's footprint is pretty small - just 15' wide - and the area based on where the toilet is and the main waste stack is, is just 5' wide. I am sure I can find it easily enough with a jackhammer, but would prefer to figure it out ahead of time.

So, are there any options?

The drain is definitely cast iron, so has anyone had luck using a Radio Shack grade metal detector?

I have read a suggestion to use an infrared laser thermometer while running hot water. Has anyone tried this?

Is there anything I can attach to the head of a snake to help trace the line? Has anyone had any luck making a DIY beacon of some sort? For example, what about using one of those radio transmitter key locator things?

Any thoughts or help would be very much appreciated!

Thanks!

Post #17, here: under-slab plumbing / DIY - Contractor Talk - Professional Construction and Remodeling Forum has an interesting idea.

24 volt encapsulated coil that you can "push" down the pipe (use an electrician's snake) and an AC digital voltmeter. Probably would prefer one with a bar graph.

Bet a 24 VAC encapsulated coil from a solenoid valve would probably work.

Renting a "sewer pipe locator" is another option.

There was an article in Circuit Cellar. Circuit Cellar Table of Contents
It might be "Innovative wire tracker" in two parts, but it's not even close to an easy build. This guy was challenged to find a break in a wire under a parking lot.

An IR thermometer will likely not work.

I've heard that this has been used to locate 120V wires. Use an inexpensive dimmer and activate a load. It spits out lots of harmonics ad then use a portable AM radio to locate the wire.

You probably still could do that. A ceiling fan dimmer to a 120/24 Vac xformer and a home made encapsulated load on the end of a wire (Say 10 W resistor) and Romex. Insert the wire and try to find it's path with the cheap AM radio. Something that doesn't mute the stations and isn't digital.

Thanks, these are some excellent idea.

Regarding the use of a 24v coil, would something like this work? How would I power it? Also, I have a pretty simple AC/DC digital voltmeter, with probes, can I get away with something like that?

Probably. Although the specs don't say 24 VAC, I believe that that would be the case. Size is yet another issue that isn't addressed. I know ASCO has some solenoid valve coils that are small. Like 1" x 1" x 1-1/4" or so. I used them. Here: http://www.ascovalve.com/Common/PDFF..._8280_2.21.pdf

A transformer such as this should work. http://support.radioshack.com/suppor.../doc9/9881.htm
You can also get 24 VAC wall wart power supplies.

For the detecting coil, if using a voltmeter, use a higher voltage coil and it doesn't have to be sealed or even use magnet wire wound on a stick. Magnet wire has a coating of a hard, extremely thin varnish insulation like Formvar. The more turns, the better.

Or use this wound on the spool it comes on. 315-Ft. Magnet Wire Set - RadioShack.com You have to literally scrape the insulation off.

What's the lowest AC scale and the resolution. Say 300 mv to 1 mV resolution?

Ignore the probes. You'll want a couple of banana plugs to connect it to the voltmeter.

Thanks so much. This seems like it could be kind of fun, actually.

Where would I go about getting the solenoid valve coil? I can't seem to find it online and wouldn't know where to go locally.

How much do you think this is all might cost? Depending on the cost, would this work?

Thanks!

The entire valve is about $32 USD from here, but it's the wrong coil voltage.

U8225B4V 120/60 110/50 - ASCO Red-Hat U8225 Direct Acting, 2 Way, General Service Sub-Miniature Solenoid Valve

Here, might be a good place to order from: 8225 Series Sub-Miniature Solenoid Valves (Asco-Valve | 2 Way Valve)

I can't find the coil p/n, but all you have to ask for is a coil for the 8280 valve with wire leads and 24 VAC. The coil is available separately and would have to be less than $32. Reminder, I've used them.

Thanks so much for all of this.

As an alternative, what do you think of the idea of using a pet finder, something like this for example. Could it work?

I think it might work. Interesting idea.

Seems like the costs might be pretty close to the same, no? Between $80 and $100. This seems suited to the task.

Do you think a cheapo radio shack metal detector would have enough depth? That's another alternative. Would it be sensitive enough. The pipe is definitely iron.

I don't know. I've got no metal detecting experience. Your probably going through 4-6" of concrete.