The best way to manage latex, acrylic, and water-based paints and stains are to
Use it up - Small amounts of paint can be mixed with other colors or bulked together
and used as a primer coat or on jobs where the final finish is not
Dry it up - Place kitty litter in with the left over paint to harden it or use paint hardening products that are on the market.
Pass it on - Donate unused paint to community projects or neighbors to be used on small projects.
Prevention is the best practice. Buy only what you need to get the job done. One gallon of paint will cover between 250 and 350 square feet.
If you have some paint left over you can dispose of it in the regular trash, but first it must be solidified. Do not place liquid paint in your trash.
Sharps or needles should be placed in a heavy plastic jug or bottle with a tightly secured lid and then placed in the household garbage. Do not place the container with the sharps in your recycling bins.