MLSS= mixed liquor suspended solids

Yes, it separates the sewage into black water and solids. The solids remain in the tank and are consumed by microbes and worms, forming a 'mattress' of semi solids that floats in the tank as black water passes out of the tank to the septic field.

It must avoid clogging of sewage pipes.

The density of raw sewage can vary widely depending on its composition and the presence of solids. On average, it can range from 1,010 to 1,050 kilograms per cubic meter.

A cesspool is an underground tank that collects and stores sewage. As sewage enters the cesspool, solids settle to the bottom while liquids are absorbed into the surrounding soil. Over time, the solids need to be pumped out and the cesspool may need to be replaced to prevent overflowing or contamination.