a settling apparatus includes a decanter having a sludge bed therein . a raw water inlet leads raw water to be treated into the decanter , such that the raw water passes upwardly through the sludge bed , whereby impurities in the water are removed in the form of settling sludge , a portion of which collects in a concentrator . a vacuum source is connected to the decanter to allow for pulsating introduction of the raw water into the sludge bed . at least one siphon extends into the concentrator and is selectively connectable to the vacuum source to withdraw collected sludge from the concentrator and pass such sludge to a sludge removal station . the siphon is also selectively connectible to the vacuum source and the raw water inlet to cause raw water to be passed through the siphon and wash the concentrator and the interior of the decanter .