plastic to concrete drain pipe

[geof]

I am replacing a kitchen sink drain line. Outside the foundation, the old, 2" steel pipe was cemented into concrete pipe. There is a straight section of concrete pipe that connects to the septic tank which appears to be in good condition so I would like to leave it in place. The concrete pipe is approximately 4 inches in inside diameter. My theory is that I could put 3 inch ABS pipe into this and cement it in place. Will this work or is there a better way ?
Thank you.

 

[Gary Swart]

I'd suggest you dig the old pipe up and replace it with 4" PVC. Concrete drain pipe is not a good choice for drains as roots can get into it very easily, and the main drain should be 4". Do the whole job right the first time and you're done with it. I question that you could insert the PVC into the concrete pipe anyway. You'd have to have a trench as deep as the drain pipe and as long as the PVC, and I can't envision how you'd do that. Just get rid of the concrete.

 

[Sponsor]

 

[geof]

Thanks for your suggestion. Replacing the whole line would be best, but better would be good enough for me now. I was thinking of just making a connection between the plastic and the concrete, not lining the concrete with plastic. This would save some digging and other work. The drain is only for a sink so I think 3" would be enough and it is more than the 2" that was originally installed.

 

[hj]

drain

3" is usually too big for a sink. The flow rate is too slow for proper self cleansing, and the pipe can fill up with grease buildup. Once that happens, in many cases, there is no accesible cleanout large enough to properly clean it out. That is why many inspectors would turn it down.

 

[geof]

Thanks for the idea on flow rate. I hadn't thought of that. The bathroom and clothes washer discharge from one line to the septic tank. The kitchen sink is on a separate line. And most of the horizontal length of that line is 4" ID concrete pipe. That pipe is mostly open so I'll stay with it for now.