What type of material does drainrock usually consist of?

Drainrock typically consists of cleaned washed gravel or crushed rock because this type of material has been specifically processed to remove impurities and dust, allowing for better drainage characteristics. The washing process ensures that the gravel is free from fine particles that can clog the spaces between larger stones, which is essential for allowing water to flow freely. This quality of being properly washed makes it effective in septic system applications, where drainage is crucial for preventing system failures and ensuring optimal functioning of the septic system. In contrast to the other options, which do not emphasize the cleaning and sizing of the material, cleaned washed gravel or crushed rock specifically meets the requirements for effective drainage and septic system performance.