3" or 4" sewer pipe?

I have to replace the sewer line from the house to the alley. The line is under the concrete patio. I would like to avoid sawing and removing concrete if possible. I was wondering if it would be a bad idea to slip a piece of 3" pvc inside the black pipe. The reducer fitting may cause some obstruction/resistance which cause clogs and defeat the purpose of replacing pipe. Is the 3" too small?

Are you saying to slip the 3" into the existing pipe? Maybe I'm reading it wrong but thats what I'm thinking. I ran into this just last week with a 4" clay footer tile with a piece of 3" cast iron shoved into it and going to the sump pit. Needless to say....leaked like a sive. Anyway, if you're saying you're thinking of just shoving one pipe into another, no, you cant do that.

The other possibility is that you're asking if you can reduce the size of the pipe using appropriate fittings. Again, the answer is no. You cannot decrease the size of a pipe in the direction of flow. The pipe is sized according to fixture unit values and decreasing the size decreases the amount of DFUs. In addition, you're right about the real possibility of obstructions at that point.

Hate to say it, but you're going to have to get under that concrete pad if you're going to dig this sewer up and replace it.

One last note. There are methods that I'm only now becoming familiar with in which your sewer is replaced without the need for digging up the yard. As I said, I'm not familiar with these methods, but others here are.

Other methods

There are other methods such as a "mole", but even if available in your area, it probably wouldn't be cost effective. You can have the concrete cut, removed, and replaced without much fuss or mess.

pipe

The answer to question depends on whether you have 3" or 4" coming out of the house. In this area almost all of the houses have 3" exiting the house and then it increased to 4". When replacing these we always stay with the 3". In your case, if you do have 3", and the existing pipe under the driveway is straight enough to slide a 3" pipe through it, you could do it and only increase to 4" at the point of connection to the city's stub.

Thanks for the info. I will have to look under the house and see if it is four inch or three inch. I am ready to pull my hair out to begin with., We just bought the house and were assured that there had been no plumbing problems. Less than two weeks after moving in we had major clog problems. Last week I pulled carpet/rug fibers out of the drain with a power snake. Needless to say the fibers are not water soluable and should not be there.

The garage was closed in and a wood floor installed about 6 or 8 inches above the concrete slab. I can't get under there to see how the fixtures were plumbed in. A laundry room and bathroom were built in the garage space. I keep hearing gurgling noises out of the shower drain when the toilet is flushed. The snake I have is 75 feet long and I think I may have just pushed the clog out to 75 feet away. To top it off i think they installed a secind line to the main in the alley so will have to go on a treasure hunt to find the line outside and install a cleanout. Wish I had the cash to have it done

Thaks again for the info.....