A sewer dosing unit (SDU) is a plumbing device to allow effective sewage disposal with low liquid-flow rates. With a global emphasis on water saving, many new buildings and renovations are seeing the installation of water saving fixtures such as low flow shower heads and low flush toilets. With the decrease in wastewater flows problems are arising from waste solids not being carried completely to the main sewers, often causing blockages.
Independent testing has shown that the use of an SDU allows for the use of low flush toilets using as little as 0.8 L to push general waste solids more than 25 metres along a typical wastewater drainpipe. An advantage of the SDU is that it can use more than just the toilet wastewater to keep drains clear of blockages.
A low-flush toilet (or low-flow toilet or high-efficiency toilet) is a flush toilet that uses significantly less water than a full-flush toilet. Low-flush toilets use 4.8 litres (1.3 US gal; 1.1 imp gal) or less per flush, as opposed to 6 litres (1.6 US gal; 1.3 imp gal) or more. They came into use in the United States in the 1990s, in response to water conservation concerns. Low-flush toilets include single-flush models and dual-flush toilets, which typically use 1.6 USgpf for the full flush and 1.28 US for a reduced flush.