What does grillage refer to in plumbing terms?

Grillage in plumbing refers to a structural base that is typically composed of sand and small gravel. This material is used to support foundations and underground plumbing installations by providing a stable and well-drained surface. The purpose of grillage is to distribute loads evenly and enhance the stability of the structures above, such as tanks or other heavy plumbing setups.

Using sand and small gravel allows for proper drainage, preventing water from pooling and leading to potential issues such as erosion or instability. The characteristics of this material ensure that it compacts well while allowing for adequate drainage, making it an ideal choice for applications in plumbing where support and stability are crucial. The other options listed, while related to construction materials, do not align with the definition of grillage in the plumbing context.