I am in the same situation with my 21 year old son.
He has had OCD (Undiagnosed) for 3 years now and refuse to acknowledge that he has it, let alone getting help either counselling/CBT or medication. He can spend ages washing his hands and cleaning his computer desk in his bedroom and sometimes spend 2 hours in the shower. The OCD has got so bad that he has got physical abusive with me from not giving him cleaning products and i have had to call the police on 6 occasions.
The only way out of this circle of refusing help i think is to call 999 and ask for hospital help. Unfortunately i have spoken to the doctors and they don't seem to care, despite the fact I've told them that my son is a danger to myself and other people.