Over the last couple of years, there has been a lot of press on city sewers backing up into peoples home. This is caused by more rain than the sewers can cope with and this occurs particularly in spring with the run off. Installing a back water preventer onto your main waste pipe in your basement can help prevent damage to your home.This has a yellow plastic float flap integrated into the unit, which lifts up when the sewage volume from the road rises, thus blocking the entry into your home.