sanitary sewer detail with floor slab on void

[geobeb]

As an alternative to a structural floor over a crawlspace on an expansive soil site, we have provided recommendations for a structural slab on a 6" void. I am looking for a detail that will prevent heave of the soil below the slab from adversely affecting the sanitary sewer lines, either by suspending the lines from below the slab or by providing a collapsible or telescoping fitting just below the slab penetration.