To rinse something out in order to clean or empty it. A noun or pronoun can be used between "swill" and "out." Be sure to swill out your cups with water and sterilizing solution after every meal while you're out here.Just swill the glasses from last night out and pour the wine into them.
swill out
v.
To empty or clean something by a flow of water or liquid: After you finish washing the dishes, swill out the sink with water. I swilled the cup out and poured myself a glass of milk.