Having read all of the comments, there are definitely some good pieces of advice here but I would be weary of some of the more overt approaches suggested. That's not to say they would definitely fail but they are more risky in my opinion. I haven't had time to read any of your other posts to see if you've given more detail of the situation or the person in question so it's difficult to say exactly what I think would be the best approach. We are complex creatures and the world we live in can be very cruel and unpredictable, so I think a carefully and well-thought out approach taking absolutely every piece of information and advice into consideration would be your best course of action. If I may, I would like to suggest that you might consider some of the following:
What is your relationship with this person?
What do you know about their personality, health (both physical and mental), background etc?
Are you certain that the rubbish is not from somebody else? Do they ever have guests to stay?
Maybe they occasionally take someone else's rubbish out and have absolutely no interest in it's contents?
Your own experience of being ABDL from start to present moment
The emotions and feelings you went through when discovering yourself
At what point in your ABDL existence would have you been ready to be approached by another ABDL?
How would have you reacted at different points in your ABDL journey so far?
Try to put yourself in their shoes and think about how they might react to any sort of approach
Advice given in some of the comments to this post
Anything else even slightly relevant to the entire situation
Pro's and Con's of any outcome you can possibly imagine
Having said all of this, there are two key elements that I would strongly suggest that you consider to include when deciding what your next move will be. Firstly, I would be extremely cautious and calculated in considering how, when and where you approach the person. I don't know how well you know them but if you're not very well acquainted, then for starters I'd try go get to know them a bit better and see if you get on as friends before doing anything ABDL whatsoever. If you're already good friends and know them well then I think you should spend at the very least, a few days weighing up your options here.
You haven't said much about the person so it's hard for me to speculate but I think it would be unwise to say that most likely both of you have something to lose here. Remember that collectively, the entire ABDL community as we know it, is so diverse that it could give the Sahara Bar from Star Wars a run for it's money! Think about the absolute worst case scenario for your housemate... there is an unknown number of closet ABDL's in existence who have no interest in ever sharing it with anybody else or even on social media; it's just for them in their own private space. Some may even be so mentally fragile and unstable that any sort of approach could upset them. Obviously this is an extreme example, but I think with something as sensitive as this, being considerate is respectful, commendable and responsible. Ultimately though, only you will know the best way to handle things as you know the person best.
Being subtle, discreet and maybe even anonymous can go a long way to prevent or minimise any potential uncomfortableness for either party - if things take a turn for the worse, then it will be so much easier to walk away and pretend it never happened. Being careful is gonna take a bit more time but will pay off in the long run if you've made a bad judgement call on this one.
Perhaps most importantly though, whatever the approach and outcome - good or bad; you need to completely and totally own whatever you say or do regarding ABDL. You should be appear 110% comfortable, confident, self-assured, and in a happy, friendly, positive mood. As mentioned in one of the other comments, your mood and approach will most likely be mirrored by this person so, whether they react positively or negatively, this mindset can only improve the situation of any possible outcome. If it's water off of a duck's back for you then there is a good chance it will be the same for them too.
I'm not sure if you know but there is a channel on youtube called BackIn Diapers. It's ran by a girl called Brittany who is both IC and ABDL. Her channel is primarily for IC support, product reviews, and advice but there are one or two videos which talk a little about ABDL where appropriate, but she always stresses that the channel is for IC support and not ABDL, which I respect massively. Anyway, there is one video where she talks about her experiences of discussing her IC and needing to wear 24/7 with friends, colleagues and family members, which you might wanna watch. She makes the point that the more confidence you have when taking about it with others makes them much more comfortable and positive. They see that you are fine with it so they usually respond in the same way and afterwards just carry on with their lives. And that is very true in my own experiences too. And thats why I think it is so important that you try to adopt this approach... I firmly believe that it can only make any situation easier.
Having said all of that - how do I know he is not already trying to drop hints to you as some others have suggested, which is very possible?
I'd say just be careful and as sure as possible... it's better to be safe than sorry!
Anyway, I hope my words will be of some use to you.
Let us know how you get on and I wish you the very best of luck!