My question is about a small joint diffusion in both knees. i have severe pain in both knees. do doctors normally drain knees for a small diffusion?

Sometimes: Usually do not unless infection is suspected. A small knee effusion is prob secondary to some trauma, arthritis. If the joints are not warm, or red, then infection is prob not the problem. The severe pain does need evaluation though, call your DR and get an apt in the next few days.

Generally no.: The small amount of excess fluid in your knees may be a result of arthritis or inflammation, The fluid itself doesn't cause pain. Only if the doctor needs a sample of joint fluid for diagnostic purpose would s'he try to remove the fluid.

Depends on a cause: you may need a tap for diagnostic purposes, but history and physical are important. Do you have reactive arthritis, rheumatoid, how frequently symptoms occur, have you had steroid injection, or this simply wear and tear? This is not simple tap or not to tap question - talk to your doctor

Effusion?: Normally they do not drain it unless they are doing it for a diagnosis. Normally they treat the cause of the pain and effusion and then the effusion will resolve. If you do not treat the underlying cause the effusion will come back. Doctors do not stick needles in a joint unless there is a reason to do it. See your doctor and have your knees evaluated.