Underslab plumbing is critical to the building process. It includes any plumbing related lines that are installed underneath the concrete slab. That may be just waste lines or both waste lines and water lines.
Waste lines must have the correct slope within the foundation area. They should also be sized according to the number of bathrooms that will be in the building. A house that has 6 bathrooms, of course, will require larger waste lines than a house that has 2 bathrooms. The pluming contractor should know exactly what is required, both in the size of lines and the amount of fall.
Water lines can be run under the slab or in the attic. If underslab, water lines should be protected from damage that can occur during backfill. Testing of water lines and waste lines should take place before concrete is placed. Test once before backfill and again once back fill and underslab prep is complete. If lines have been damaged during backfill, it is important to identify it prior to pouring concrete.