Your grandson isn’t the only child with an ASD that displays this pattern of urinating in inappropriate places. This is most difficult to treat if it happens at night while you’re sleeping. If it’s in the same place (e.g., in a clothing hamper), sometimes just removing the item that he urinates on can be helpful. I am assuming that these aren’t just accidents but sometimes it can also help to make sure that he is toileted on a regular schedule and watch his fluid intake before bed (if the issue happens overnight). If he understands contracts, placing a contingency where he can earn something special for each set period of time without any inappropriate urination can work. My recommendation is to speak to a board certified behavior analyst about the specifics of the problem.