True... it has to become the "dye pot." Here's something that blew my mind though...
I have one of those enamel on steel canners, the dark blue/black with white specks to use as a dye pot. I'd used it with Gay Wool several times, then tried some Kool-Aid, just for fun. The enamel surface was...
If you have a large pot (like for canning), access to a stove and sink, you can dye wool in small batches. I got a window screen (make sure it's not metal) to lay over the sink for the wool to drip dry. Then I put it in a mesh bag and hung it over a furnace vent to finish drying.
You can dye wool at any stage of the process. You can dye wool that is already dyed, to change or tweak the color.
Wool, being a protein fiber, needs an acid dye. Interestingly enough, good ol' Kool-Aid will work.
If you want to do a lot of it, I highly recommend the Gay Wool line of dyes...