An apparatus for dewatering sludge comprises a tank having an internal space divided by a dividing wall into an intake chamber and an extract chamber, an intake pipe connected to the intake chamber by an intake valve, a discharge pipe connected to the extract chamber by a discharge valve, and a transfer pipe providing fluid communication between the intake chamber and the extract chamber. The transfer pipe has first opening near the bottom of the intake chamber, and a second opening near the top of the extract chamber. A pump selectively creates positive and negative pressure within the intake chamber. A screen is positioned within the extract chamber between the second opening of the transfer pipe and the discharge pipe.