I see nothing wrong in slipping the 4" PVC through the 6" clay pipe as
long as there is continuous fall on the pipe (since you're using it as the
invert.) Hopefully there is nothing wrong with that section of pipe as it
will save you time and money. Avoid any joints in this section (not knowing
how long it is.) Just remember that the clay pipe you're looking at might
very well be 4". The wall thickness of clay pipe is so great, that it may
appear to be 6" - a very common error - even by some pro's in a hurry. For
your sake (and the sake of not removing the concrete steps) I hope it is.
:-)

Don't forget to install a cleanout plug at every 90° turn of direction
and at least every 50'. Most people like to run 75' - 100' for their clean
outs, but I've found that most places that sell cables to the homeowner come
in 50' lengths. You might even consider a two-way cleanout about mid-line.
Just a thought . . .

Jim



"jeff" wrote in message:
When installing a new sewer line at my house, the goal is a complete 4"
sch40 PVC mainline connection from the house to the curb, except that, in
one small section, in which a concrete staircase is over the pipe, they're
considering slipping the 4" PVC through through the existing 6" clay pipe
(assuming the current outside line is 6" clay.)

The line within my house is already only 4" line, and 4" PVC is what they
normally install around here for new residential lines as permitted by the
code. If so, then slipping the 4" Sch40 PVC through existing 6" clay
pipe
is being considered for the problematic section where the concrete steps
are
located. The end result would be a completely-PVC connection from my
house
to the curb, except that one section of the PVC pipe would happen to have
the old 6" clay pipe around it.

Would this be considered improper or is this acceptable?

Jeff