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I live in a housing addition (built 1965-1980) in the barren (no trees) Oklahoma panhandle. The first thing the new home owners in this area did was plant as many trees as possible.

Over last several years in my neighborhood many of these house sewer lines out to the alley main line are being dug up to replace either rotted (cast iron tree rooted pipe) or collapsed schedule 20 PVC (yes 20 not 40 schedule).

I guess my line is PVC because bent cloths-hangers & rented metal pipe finders won’t even blink to indicate cast iron. So knowing that at any time now it will be my turn to destroy my heavily treed back yard to replace my sewer line.

This town is trying to die & most plumbers have retired or moved off & not one of the remaining plumbers has a camera or pipe line sensor to run down the closet toilet to locate the line out in the yard. Also, there are no clean outs in yard which could indicate where to start digging.

My Question:

The next time it snows, if I pull the toilet off of the closet flange, configure a 4” to 24” square metal HVAC pipe duct funnel, set a 24” x 24” box fan on top of funnel, turn the central heat up sky high & blow hot house air down funnel into sewer line, would I be able to melt the snow so I can see where the pipe runs?

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    Hot water would do better than hot air and not involve any yanking toilets and letting sewer gas into the house - try doing several loads of laundry that use hot, run the dishwasher or do the dishes, take a hot bath, etc. - but not likely to show up from 3 feet down, really. Drive to someplace that rents the tool you need is more likely to work.
    – Ecnerwal
    Jan 31, 2023 at 18:16
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    Should work in a couple of weeks. Imagine the ground is quite frozen solid by now, so you need to warm the pipe, the ground before any snow will start to melt. The city/town might maps of where the house sewers connect to main pipe. The line should be in a straight line from where exits the house to there. The exit from the house will be a good starting place for digging.
    – crip659
    Jan 31, 2023 at 18:16
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    Why do you need to pop the toilet off the flange? Just remove the toilet seat and you should have a nice flat surface for a piece of plywood and some caulk. When done, the caulk will release cleanly from the porcelain enamel. However your bigger problem is the sewer vent pipes all over your house. Hot air will simply go up those. That's where water has the edge. Jan 31, 2023 at 21:20
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    Oily Tex, Consider if the heat of the heated drain pipe could significantly affect the snow cover, then the snow cover could affect the drain pipe. IOWs, it this works, the drain is not deep enough to prevent its freeing during normal usage. Feb 1, 2023 at 14:38
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    For what it's worth, I've lived in three different houses with septic systems and a snowy climate. In every case, the location of the septic and pump tank was very clear soon after a snowfall, but the location of the sewage pipe from the house to the tank was never visible. I think it's just too deep.
    – Mark
    Feb 2, 2023 at 0:37

5 Answers 5

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I doubt that you could get enough heat into the sewer line to melt the snow on the surface. Even if it did, that would only give you a vague idea where the pipe run is, though it would be more accurate than nothing.

I've got two alternate suggestions:

  1. Ask the city. They'll know where the main sewer line is and, most likely, they'll know where your house is connected to it. Once you know where that point is, it's highly likely that the drain line runs straight back to the house in the shortest distance possible. Construction companies don't like to waste time and material making random routes when a straight line will do.

  2. Rent a snake long enough to reach from your toilet to about 1/2 down your back yard. Run the snake down the drain, then use a metal detector to find the snake. Once you've got a good idea of location and direction, it's probably safe to presume that the run will continue in a straight line unless there's an obvious obstacle (that was there when the subdivision was built, not something added afterwards).

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    DUH, ! ! !, WOW, OK. That’s so simple. Just pull toilet & run a snake down 4” line & out under back yard. Go back to United Rental @ Liberal Kn & re-rent metal detector. Flag the high toned beeps out to the alley. Problem solved. FreeMan, I know I’m not supposed to say THANK YOU, but I can’t help it ( THANK YOU ) also to crip659 & Jack. You guys are the best, Oilytex.
    – Oily Tex
    Jan 31, 2023 at 19:43
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    @OilyTex: We just ask that you make the thank yous in comments, no thank you "answers". :-D Feb 1, 2023 at 3:25
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    You might want to look at a utility locator with a separate "toner" (cable line transmitter). You attach the toner to a metal pipe or in your case a drain snake and it turns it into a radio antenna broadcasting a signal. The utility locator can then detect the signal more accurately then the metal detector method.
    – John Ray
    Feb 1, 2023 at 7:49
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    They even sell (and probably rent out) pipe locators. I don't know how accurate they are (never used one) but it sounds pretty promising. Feb 1, 2023 at 14:55
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    Option 2 above is how they figure where to cut the sewer line for a plumbing disconnect in my city.
    – shoover
    Feb 1, 2023 at 15:43
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Tl;dr: physics says it's going to be very expensive.

Lets run some extremely rough numbers. This is going to approximate a lower limit on the heat required - you're likely to need far more. I've rounded massively, and more often than I should.

I'm going to assume a pipe buried 1 metre down, in soil that's at 0°C covered with a thin layer of frost/snow - just enough to indicate the temperature rise by melting.

The volume of soil that needs to be thawed will be considerably greater than the volume between the pipe and the surface, as the ground will conduct heat in all directions equally. I'm going to say you need to thaw a 3 square metre cross section (πr² with r=1m from the depth, rounded).

Dry soil has a density of around 1200kg/m³; the moisture content is likely to be 10-50% of this. With rounding that means 100-500kg of water per cubic metre, or 300--1500kg per metre of pipe run.

The latent heat of melting of water is 334kJ/kg, call it 300kJ/kg. That means for each linear metre of pipe, just to thaw the water in the soil if it's already at freezing point, you'll need 90--450MJ. 1kWh is 3.6MJ, so you'd need to deliver something like 30-150 kWh per linear metre of pipe.

This will go up if the soil is colder than freezing point, but not by all that much. The specific heat capacity of ice is 2.1kJ/kgK, so for each degree Celsius below freezing you'll need an extra 0.6-3MJ.

A thick layer of snow will make things far worse. Snow is a good insulator so more of the heat will go into the soil and less will reach the surface.

Lets see how much hot water you'd have to deliver to achieve that. A full bath holds the best part of 200 litres. At 60°C, cooling to to 0°C (which you won't manage) that's 50MJ (or about 14kWh, or £1.40 at UK gas prices). That means you need at least two very hot, full bathtubs per metre of pipe run.

At the price I pay converted to USD that's $3.40 per metre in heat - if you can deliver it with as much efficiency as I calculate, which you can't (and if the soil is exactly at freezing point, though this is a small effect). You could easily be into the tens of dollars per metre. You imply a fairly large plot of land, so you could well be into spending thousands of dollars on heat with no guarantee of success.

I wonder how much it would cost to hire ground penetrating radar; even with an operator it's probably cheaper and has a far higher chance of success.

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    BTW I can see where your thinking comes from. In my street the snow melts far quicker (or frost doesn't form) around the inspection hatches for the sewer. However instead of a big volume of soil, the heat from the pipe only has to warm a smaller volume of air in the inspection chamber. Between the covers, knowing the pipe run, I've never seen waste heat prevent frosting, even though by this point it's the waste heat from a dozen houses, and even ons night when the temperature drops only just low enough for frost to form.
    – Chris H
    Feb 1, 2023 at 10:41
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    Clarify please - do you need to do this now, in winter? Or can you wait till next spring when the ground is diggable, and then get stuck-in with a spade where the sewer line exits your house ?
    – Criggie
    Feb 1, 2023 at 21:57
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    The thing is you don't need to melt the snow with the heat. What you want to do is wait until snow is naturally melting and add a little bit of energy so the snow above the pipes melts faster.
    – user71659
    Feb 2, 2023 at 0:49
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    @user71659, that doesn't gain you much. Soil is a wonderful insulator, so it takes a lot of heat to raise the temperature of the surface even a little.
    – Mark
    Feb 2, 2023 at 1:19
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    user71659 That’s a good suggestion. If I waited for the melt to begin, as the ground starts to warm, then the extra hot water energy would help Mother Nature due her thang. All I would need is just a slight impression & red flag the sewer line out to the alley.
    – Oily Tex
    Feb 2, 2023 at 1:22
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I seriously doubt that running air from your heating system down a pipe 36" below grade in freezing weather will melt snow at grade level. Most counties, townships, etc., have phone numbers to call for locations of underground facilities. Try them. Check with other neighbors and see how their pipes were run in relation to their toilets and out their walls and make an educated guess on where your pipe exits the wall and dig a small hole to verify a location. Fom there, dig along the exposed pipe to the alley. You could also try contacting separate underground location companies. Some can run a sensor thhrough the pipe and then trace the signal above ground.

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  • Ecnerwal, Adding to your plan of attack. You really got me & neighbor thinking ! ! ! I got 4 Bathrooms & 2 water heaters, so me & neighbor are going to fill 2 tubs with scalding hot water, pull toilet off back of house & connect his ( Dewalt 45,000 BTU, MASTER BLASTER, forced air portable propane heater to the closet flange, fire up the heater & pull stoppers on both tubs at once. The hot water & propane, should really get a good conductive heat wave cranked up, and keep propane going between required tub fillings TILL THE COWS COME HOME, I think this might work.
    – Oily Tex
    Jan 31, 2023 at 19:15
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    crip659, I have all ready went to city hall, they said they never started the program where they mapped the utilitys going to homes & business, but said they should have done that in hind-site
    – Oily Tex
    Jan 31, 2023 at 19:22
  • Jack, last year I contacted a line finding company in Amarillo Texas (120 miles away) & they turned me down, said it would be very expensive, & besides that, they didn’t want to risk their lives coming to the Oklahoma Panhandle ! ! !
    – Oily Tex
    Jan 31, 2023 at 19:25
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    If you pump that much hot air down your sewer, I think you risk softening and collapsing your sewer lines. Bad idea.
    – longneck
    Jan 31, 2023 at 20:50
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    I also wouldn't fancy dropping lots of water in while trying to blow in air - in some conditions some water could end up coming out into the space heater
    – Chris H
    Feb 1, 2023 at 10:00
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I recently had a plugged PVC sewer line and had to run a 100' snake down it. I was having trouble locating the cleanout downstream. So, I sent the snake down the line and ran it with someone else in the area of where we thought it might be and could hear the snake very clearly underground. If you want to identify were the line is, I recommend renting a snake for roughly $50 and doing it this way.

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    asp316: Are you saying that by dragging the snake in and out of the sewer line, you were able to hear the dragging sound resonating up through the end of the burried clean out line just below the surface. My neighbors have exposed clean outs, but if there is one in my yard, it’s burried. If this works, (providing I have a clean out), it could sure show me where to start backhoeing. Maybe wouldn’t have to wait for the next snow.
    – Oily Tex
    Feb 1, 2023 at 0:21
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    @OilyTex If you can't hear where the end of the snake is, maybe you have a dog who would let you know where it is. Feb 1, 2023 at 19:07
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    @OilyTex - Don't move the snake in an out, but just push the pedal to turn on the snake and let it turn in the pipe. As it turns, have someone else walk along where you think the pipe is, remembering about how far in the snake is. You'll be able to hear the tip bouncing around inside the pipe from above ground. My cleanout was buried also, but had a rough idea where it was. I used a tree feeder to push into the ground until I hit the cap.
    – asp316
    Feb 2, 2023 at 21:01
  • asp316 Yea, that makes since, slider in & rotate it so it will flop around. Should make lots more sound than pulling back & forth. Good idea.
    – Oily Tex
    Feb 3, 2023 at 0:40
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I'd be tempted to try audio. Buy a rape alarm: they're cheap, small and loud and if you lose it, it'll probably flush away. Take the connector off the end of a garden hose and attach the rape alarm to the hose securely. Set the alarm off and push the hose down the toilet. Go outside and listen - maybe use a stethoscope, they are cheap too.

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    I'm not sure you'd hear it through 3 feet of dirt, but then again, someone said they could hear the snake in the line, so it's got potential...
    – FreeMan
    Feb 3, 2023 at 17:51
  • FreeMan, that is reall a cool idea, & may be a (1st ever). Maybe Chris H or Ecnerwal will chim in on this. Yea, if you could maybe hear the rotating snake, then this would really worth trying. I could borrow the neighbors German Shepherd. That dog can hear everything.
    – Oily Tex
    Feb 4, 2023 at 0:22

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