Toilet plumbing is done in either of two ways: using a drop slab, or with underslung plumbing.

In a drop slab, the slab below the toilet is 'dropped' or built about a foot below the rest of the slab. This forms a kind of tub in which all the plumbing for the toilet is laid. Once it is laid, the entire tub is filled up with a concrete-based filler material, and tiles are laid over the filler material. The plumbing is entirely encased within the structure and is not accessible.

In underslung plumbing, the toilet slab is built at the same level as the slabs outside the toilet. Holes are punctured through the slab wherever pipes have to pass through, and the plumbing is clamped to the bottom of the slab. It is then concealed above a false ceiling, but of course, is accessible behind the false ceiling. In this type of plumbing, any leaks will drip onto the false ceiling and then onto the occupants below! The upside is that leaks can be repaired, or the plumbing entirely replaced, without disturbing the structure.