Blot up spills with an absorbent, lint-free rag or towel as quickly as possible. Also, vacuum dirt, dust and other loose debris quickly before they set in, as they can slowly darken the round cushion.
Spot treat stains. Select upholstery cleaner appropriate for the fabric covering the round cushion and use it according to manufacturer's directions. Typically, it's best to spray any cleaner first on a clean, lint free rag then rub it onto the stain gently in a back and forth motion, working from the center to the outer edges of the stain. Repeat with water to rinse.
Take off the round cushion's cover, if possible, to launder it according to the consumer care tag. However, some manufacturers do not recommend this, since it may too difficult to get the cover back on. Always read the tag or care instructions that came with the cushion carefully. Air dry the cover so it does not shrink or lose some of its shape. You can also wash the entire cushion this way if the cover does not come off and if the care label's instructions state that the entire cushion is machine washable.
Hand wash the cushion itself if it is soaked with urine or another substance that has must be removed. Fill your sink or tub and saturate the cushion and wash it with a little bit of laundry detergent. Swish, squeeze and gently agitate the cushion to clean it. Repeat with clean water to rinse. You may need to rinse it a second time. Gently squeeze out the excess water, being careful not to rip the cushion in the process. Let it drip and air dry in a warm and well ventilated area. You can also carefully use a hair dryer to help the round cushion dry.