How can I get rid of fluid on the knee?

Go to Dr. Try elastic support either with knee elastic brace or wrapping with ace bandages, but most likely you need aspiration of the fluid with a needle/ syringe done by a rheumatologist, an orthopode ( especially if the knee was operated) or a pcp (primary care physician )that feels comfortable doing it. Apply cold if recent injury, warm if chronic. Also r.I.C.E. (rest, immobilization, cold, elevation).
Ice, bike, NSAID . Joint effusion or excess fluid in the knee is usually from a flare of arthritis or trauma but could also be from an acute injury to the meniscus or acl. Moving the knee with low or non- impact exercises ( like stationary bike) will help put ice behind and in front of the knee after exercise or work. Take an antiinflammatory like Ibuprofen for 5-7 days ( with food).