Verifying Pipe Size on a sewer line

[Kent Harris]

I recently had a plumber come out to fix a broken sewer pipe under the foundation. After the house flooded a second time with raw sewage the second plumbing company found mud in the pipe the first plumber did not clean out. The first plumber said there was another break in the line causing the issue. I hired the second plumber who scoped out the line and did not find a break in the line. The second plumbing company said that the risers was drain pipe and not sewer pipe. I noticed there was a collar that went from a smaller pipe to bigger pipe at 12 feet where the line had broken. The owner of the first plumbing company came out and told me it was 3 inch pipe were it broke and they replaced it with 4 inch pipe going out to the sewer main.

The inside diameter of 4 inch drain pipe is a little wider then 4 inch sewer pipe. My question is. How can I measure the inside diameter of the pipe without having to dig up the line? I would think if I put a ball with a string inside the pipe if it were drain pipe it would go through if it were sewer pipe it wouldn't. There must be some type of device to measure the diameter of the pipe from the inside.

The second plumbing company did not want to get involved so they wouldn't tell me anything other then the risers were drain pipe.