The present invention provides a method for efficiently filtering slurry suspensions in a vessel including a nozzle flange near the vessel, when solids in the slurry suspensions being treated in the vessel are filtered for cleaning or for other purposes and subsequently subjected to reslurrying, dissolving or dispersing operation. A method for producing suspensions, solutions or dispersions comprising separating solids from slurry suspensions and then slurrying, dissolving or dispersing the solids again by adding a solvent, characterized in that the above described solids are separated in the same vessel as the one in which the operation to obtain the above described slurry suspensions has been performed and/or inside a flange directly connected to the same vessel.