J.W.
He wants to use the potty, let him. Yes it's frustrating, time consuming and challenging with his limited communication skills. Training pants (thick cotton underwear) or pull-ups coupled with elastic waisted pants, easy down and up efforts for him to have some control over when he needs to go to the bathroom.
May I suggest Child Speaks, it was formerly called Scottish Rite Center for Childhood Language Disorders. They are mircacle workers, their speech therapists, teachers of sign language... giving kids a means of communicating. I can't begin to sing their praises loud or often enough. They have offices in Seattle, Spokane, Yakima and Portland that I know of for certain.
Take good care.