Method for operating a washing machine , the washing machine having a suds container , a valve , a reservoir for temporarily storing washing liquor when the washing liquor is pumped out, and a suds pump for pumping washing liquor out of the suds container via the reservoir in the direction of a water drain , the valve being designed to prevent washing liquor in the reservoir from flowing back into the suds container , the method comprising the following steps: conveying washing liquor from the suds container via the reservoir in the direction of the water drain by means of the suds pump at the end of a washing process, an amount of washing liquor remaining in the reservoir after the suds pump has been deactivated; and either returning the washing liquor remaining in the reservoir into the suds container for use in a subsequent washing process, depending on a residence time of the washing liquor in the reservoir ; or discarding the washing liquor remaining in the reservoir via the water drain depending on the residence time of the washing liquor in the reservoir ; with a step of carrying out a threshold value decision with regard to the residence time of the washing liquor in the reservoir using an adjustable threshold value, either the step of returning or the step of discarding being carried out depending on a result of the threshold value decision; with a step of detecting the residence time of the washing liquor in the reservoir by means of a time span measuring device; characterised in that in the step of discarding, the washing liquor remaining in the reservoir is flushed out of the reservoir by means of the suds pump by fresh water being introduced into the suds container and the introduced fresh water being conveyed from the suds container via the reservoir in the direction of the water drain . conveying washing liquor from the suds container via the reservoir in the direction of the water drain by means of the suds pump at the end of a washing process, an amount of washing liquor remaining in the reservoir after the suds pump has been deactivated; and either returning the washing liquor remaining in the reservoir into the suds container for use in a subsequent washing process, depending on a residence time of the washing liquor in the reservoir ; or discarding the washing liquor remaining in the reservoir via the water drain depending on the residence time of the washing liquor in the reservoir ; with a step of carrying out a threshold value decision with regard to the residence time of the washing liquor in the reservoir using an adjustable threshold value, either the step of returning or the step of discarding being carried out depending on a result of the threshold value decision; with a step of detecting the residence time of the washing liquor in the reservoir by means of a time span measuring device; characterised in that in the step of discarding, the washing liquor remaining in the reservoir is flushed out of the reservoir by means of the suds pump by fresh water being introduced into the suds container and the introduced fresh water being conveyed from the suds container via the reservoir in the direction of the water drain . <EOS>