There’s a couple ways I see it. Make the negative consequence or positive reward enough that he makes the effort to remember on his own.
You could also talk him through what happens when bin night gets missed. Where does he think the trash will go? How often does trash go out and how quickly do the bins fill up? How long does it take to catch up on a missed night? Maybe don’t rescue him when he forgets and make him figure out the answer to those questions.
There was a ghost!