Plumber tells me my drain pipes in the slab are leaking... I see no evidence of this. How do I know if they really are leaking under there?

If everything is shut off, and you are sure none of the valves don't leak, look at the water meter to see if it is moving. Now, turn the main house valve off. If there is no movement. In the meter but movement when the valve is open, you have a leak in or under the slab.

If everything is shut off, and you are sure none of the valves don't leak, look at the water meter to see if it is moving. Now, turn the main house valve off. If there is no movement. In the meter but movement when the valve is open, you have a leak in or under the slab.

It's a drain line, not a supply line. The meter isn't involved, is it?

It's a drain line, not a supply line. The meter isn't involved, is it?

OOPS missed that, sorry. Open the outside cleanout and flush a toilet. What happens? Clean water flow or muddy water? What was the issue that caused the plumber to say that? Having backup issues? Did they snake the drain and get mud or a blockage?

The property is a duplex. I noticed when water is run in the master bathroom water appears on the outside of the foundation about halfway down from the siding to the ground. The lot slopes and this end of the house is about 3 feet off the ground. The first plumber used a camera to diagnose. I watched the screen while they did it and the camera went under water in the pipe and then came back out. They said it meant the pipe was bowed and because there was no break visible it probably had pulled loose from a joint and that was causing the leak. They wanted to jackhammer the slab from inside the house to get to the pipe. I wanted a second opinion. I called a plumbing company that is a "sister company" to a long time, well respected foundation company in town. They wanted to do a "whole house leak test" on both sides of the duplex. They said they did the test by filling the lines with water and then pulling a toilet to watch the water level. If it went down it meant there was a leak. They then isolated each section of line by "blocking it off", refilling the line with water, and again watching the water level. They determined that I had 2 additional leaks, one on each side of the duplex, at the point where the hall bathroom connects to the main drain line, on both sides. Their solution was to tunnel into both sides of the duplex to fix those leaks and tunnel into the back master bathroom to fix that one. I am leary because I have never seen any evidence of the additional two leaks they found. FYI, the test took 2 men so long it cost me $656.00.