What term best describes the solid waste that accumulates in a septic tank?

The term that best describes the solid waste accumulating in a septic tank is "sludge." Within a septic system, organic materials, dead bacteria, fats, and other solid particles settle at the bottom of the tank, forming this layer of sludge. This accumulation is an essential aspect of the functioning of a septic system, as it helps separate the solids from the liquid waste, allowing for the treatment of the liquids as they move into the drain field.

Effluent refers to the liquid waste that is treated and eventually discharged from the septic tank to the drain field, rather than the solid waste. Leachate signifies liquid that has percolated through solid waste or soil, typically used in the context of landfills or composting, and is not specific to septic systems. Filtrate is a term used more broadly in filtration processes and does not apply to the context of septic waste. Therefore, sludge is the correct term for the solid waste layer found at the bottom of a septic tank.