What to do with leftover dye...

I like to mix thickened dyes and refrigerate them until ready for use. This eliminates some of the potential exposure to dry dye particles. Activator, which is used to make the dye react chemically with the fiber on the molecular level, is added just before use. Thickened dye that's been stored doesn't last forever, and sometimes I'm left with a batch and also a lack of focus on other painting possibilities. The solution: paint stripes! Paint doodle pillow fabrics! Don't underestimate the power of color-- endorphins awake! No need to discard...

empty dye containers, intense colors even when diluted by a pint of water.
In this expended form, there is little impact on water systems, according to various books I've read.

Doodle pillow fabrics