Just recycle them.

You are likely the one getting more free milk here.

I once lived in an apartment building and the guy downstairs was so extremely disgusting (cats drinking from milk in bowls of cereal he ate the night before) so I wrote a letter to the landlord explaining ALL that I saw (he left his door open often) and that we were now seeing roaches in my friend's unit across the hall from me and that I would not be happy if roaches started to appear in mine.  

People always think landlords are just out to milk the place, and maybe she just needs confirmation that you really do care but you have to protect yourself.  

If he walks the streets collecting recycleables, he needs to do that.

I will purchase four bags of softener salt and personally deliver and fill the softener myself on the 13th of August during my trash and recycling can safety/replacement inspection.Thank you once again, and please do not hesitate to contact me with any issues or questions at all.Thank you!"

But the bottom line is they played it out all the way to the end instead of just moving out.Which means if they do run into trouble, they've got no place to go and are just going to milk the free rent.Time does not heal all.

Two carts for regular trash, two for recycled, two for yard waste.  

I would also include something about the exterior- we have local ordinances about porch/yard furniture having to be outdoor furniture (to keep people from the classic couch on the porch), when and where to place garbage bins and recycling, and keeping the yard cleaned up (no garden or solo cups and beer bottles etc).  

Be sure to give them a deadline to fill it out as well.Let them know when trash and recycling is picked up and where to place it.