Ancient civilizations like the Egyptians, Greeks, and Romans understood long ago the importance of sanitation and wastewater management, building elaborate sewage systems by using underground drainage channels to carry wastewater away from their cities. These systems relied on gravity to transport wastewater to nearby bodies of water, since water cannot flow upward without being pumped. Today, many sewage systems continue using gravity in a similar way, with a suitable slope that facilitates the flow of wastewater downhill to treatment facilities or other infrastructure. This also occurs inside private lots, where a height difference is needed between the building's piping and the urban drainage or sewage system. But there are times when the available height difference is not sufficient, or when the system is lower than necessary, causing gravity to get in the way, and making the system impossible to function in turn.