Sullage system
A sullage system (or greywater) disposes of the domestic waste from kitchens (via a grease trap), baths, showers, basins and laundries.
A grease trap is a small tank, usually installed close to the kitchen, to take greywater from the kitchen sink and prevent grease entering the trenches.
You should clean the traps every three to six months and call the plumber if the trap is blocked.