Help Finding Main Drain!!!

[moore1289]

Hello All!
I hired a plumber to find my main drain, and they used a fancy snake instrument with a locator tool and they marked the floor where my main drain is located and where it exits the house.

However, when we demo'd the basement floor and dug down 20", we have not found the drain. We have a hole about 20" x 16" and are scratching our heads on what to do at this point.

We located these sewer drawings from the state government archives, but don't know how to interpret them. My house is built onto a hill, so we are wondering if its possible that the drain is just really deep?

Thanks for any help or guidance!

 

[Reach4]

I hired a plumber to find my main drain, and they used a fancy snake instrument with a locator tool and they marked the floor where my main drain is located and where it exits the house.

A fancy instrument would have also given the depth too

However, when we demo'd the basement floor and dug down 20", we have not found the drain. We have a hole about 20" x 16" and are scratching our heads on what to do at this point.

20 inches is not deep. Is the digging hard?

Consider trying a soil probe /probing rod, such as is used to locate septic tanks. Or get a better spade or post hole digger.

 

[Sponsor]

 

[James Henry]

Start a trench a couple feet on both sides of your hole the width of your shovel and keep digging. The book you found are elevations calculated from a known bench mark.

 

[Reach4]

Start a trench a couple feet on both sides of your hole the width of your shovel and keep digging. The book you found are elevations calculated from a known bench mark.

Could that benchmark be the top of the foundation? I see "Cut from top foundation" on the left page.

I see a grade rod is a rod marked in inches.

Could the "grade rod" column be how far down with respect to the ground surface (grade?)?
Or maybe the change in grade rod numbers (4.54) is the number of feet of drop between the two points on the sewer pipe path. Just speculating. I am not a pro.

Also, once you get down to the sewer line in the basement, what do you plan to do?

 

[moore1289]

Thanks all! I suspect the device did give info on the depth, but I didn't think to ask (at the time). They were also quoting the project itself, so they weren't super forthcoming with details.

The digging isn't easy due to a lot of rocks, but nothing out of the ordinary and we have the equipment to do it. We just were starting to second guess the location of the pipe since we didn't find anything!

 

[James Henry]

Could that benchmark be the top of the foundation? I see "Cut from top foundation" on the left page.

I doubt it. They wouldn't use a house foundation for a benchmark, it's not reliable. "CUT FROM TOP OF FOUNDATION " sounds to me like their talking about "cut and fill" which would be referring to excavation work for drainage or laying pipe, I can't tell from that picture. if you've ever seen a something that looks like a medallion in a sidewalk or on a concrete pad next to the road, that's a documented benchmark, manhole covers can be a benchmark. If a house is being built next to a road they will use the crown of the road as the benchmark to determine the elevation of the foundation.
if he digs a trench perpendicular to the pipe he's looking for chances are he'll find it.

 

[Reach4]

Thanks all! I suspect the device did give info on the depth, but I didn't think to ask (at the time). They were also quoting the project itself, so they weren't super forthcoming with details.

Did you pay for the locating? If so, I would expect they would give you the depth info if you ask now. If you did not pay, they would probably want some money.

If you have cast iron there, a conventional metal detector could be helpful. You may have a friend with a decent one.

 

[moore1289]

Yes, I did pay for the locating. I can try to call now and see if they have records of the depth.

 

[moore1289]

They don't have the records, and are looking to see if they kept the video from the scope/location, but they doubt they have it. I should have thought to ask!!! I won't make that mistake ever again!

 

[Dj2]

Dig a few more inches, it could be just below the footing (24" deep in most houses on slab).

 

[moore1289]

@Reach4 We are planning to add a bathroom to the basement, so we are planning to tie into the main drain with a toilet, shower and sink (with appropriate vent pipes).

 

[Reach4]

The guy who did the locating may know the range of depths he expects in your area.

@Reach4 We are planning to add a bathroom to the basement, so we are planning to tie into the main drain with a toilet, shower and sink (with appropriate vent pipes).

Given that, maybe you could explore with an auger bit or a drill. Any clue as to what pipe material you will be tapping into? PVC, cast iron? If cast iron, you could look for electrical conductivity to a ground from the bit, but not while chucked into an AC-powered drill.

If you hit a rock, that would stop the drill from progressing. You could drill thru sand or clay.

You could see how a fence pole digger worked for you. That keeps you from having to widen the hole as much as you would for a spade.

 

[moore1289]

Update: We found the main drain "Lateral Tap" yesterday. We dug down about 28" then as we were frustrated we happened to see it barely showing through the side of our hole. It ended up coming in at an angle just as the sewer engineering drawings show, and is 17" below the slab. Thanks to everybody for the help!