There is not easy response to this question as I am not certain to the kind of disability to you have referenced. If your son has an IEP- special education plan- then you may wish to ask the special education multi-disciplinary team to write in goals about hygiene or ask for assistance as part of the plan. More than likely a school nurse/ health assistant will become involved. An Occupational Therapist also may be the person who will provide your son with some kind of training or techniques, depending on his disability.
However, a teacher being required to "clean him" is in my opinion, unlikely. Since I have not seen a question quite like this before please help other parents by letting us know the outcome, if you are so inclined.