Potty training. Take 1,344,453.

My two oldest boys who are 4 and 5 are on the austism spectrum. And i'm having one HELL of a time trying to potty train my oldest. He is the one on the lesser side so he's not as behind as his brother. This past year he has really started opening up as far as trying to talk, forming sentences, following directions, etc. But this potty training is killing me. I dont know how to get him to understand that you NEED to pee in the potty. And that wet underwear is not a good thing. I'm just frustrated so off to google I go. Hopefully i'll be able to update here with progress. My goal is to have him potty trained before kindergarten starts in September.