We have a couple of chins that are prone to eye irritation. These chins get their eyes cleaned out with artificial tears after each dustbath, and then for a couple of days afterward. No exceptions. This really has helped them alot. I'd suggest doing that, and also cutting down on the frequency of dustbaths as well. Don't keep the dust pan in the cage all the time, as the dust can get contaminated with urine, etc. That could add to the problem.
Even though this is an intermittent problem, it is an ongoing one, and I think you should take your chin to the vet, and have his eyes examined. There could be an issue here that you're not aware of, and you could get some more definate answers. Your vet might know of a more effective eyedrop, too. Have your vet check your chins molars as well, as this area is not one that we can check out thoroughly at home. Their mouth is just too small for us to look that far back without a scope.
Eye problems are very uncomfortable for a chin, just like for a person. If it is irritating your chin enough for you to consider using an elizabethan collar, I think you owe it to him to consult a vet to help you with your problem solving here.and come up with an effective preventative plan.