underslab conduit run

[mshields]

I'm running a 3 over 3 4 inch PVC conduit under the slab of a building. At one point, there is a sewage pipe that affords me 18 inches of clearance between it and the slab. i.e. I need to thread through there. How should this be done? Should I put some kind of insulating material between the sewage pipe and my conduits?

Thanks,

Mike