The slow cookers that I purchased are oval in shape and quite shallow. If I had my preference, I would have liked to buy a slightly larger size and possibly a round shape (hoping that the round ones would be deeper, to make it easier to dip dye the yarn)

Also, the magenta or red colour dyes require a higher heat than the cyan or yellow, to absorb properly into the yarn. Crockpots don't always give a very good high heat, so it is best to heat the water on the stove. The slow cookers that I bought are not able to be used on the stove as well, so I have to use a regular cooking pot for the magenta dyebath.

(I use CIBA Acid Dyes) and 2 Crockpots and one regular stove pot - 1 Crockpot for Cyan, 1 for Yellow and Magenta in the stove pot.

Fill the Slow Cookers with Hot Water
Turn the Slow Cookers onto the Hot setting
Add a Tablespoon of Vinegar
Add Dye to the Slow Cooker
Wind the yarn into dye skeins and tie loosely in several places, so that the skeins don't tangle once they are in the dyepot. I wound skeins of approx. 25 grams each.
Rinse the skeins in hot water and make sure they are thoroughly wet, or the dye will be uneven.
Place the wet skeins into the dyepots and let them sit for about 20 minutes to absorb the dye. Stir the dyepots frequently in order to get even colour distribution.

To get additional colours, remove 2 dye skeins from the cyan dyepot and place 1 in the yellow dyepot and 1 into the magenta.
Similarly, remove 2 from the yellow and place them into the cyan and magenta.
And remove 2 from the magenta and place them into the cyan and yellow.

Let them sit in the dyepots for about another 10-20 minutes.

You can continue to move skeins from one dyepot to another to get different colours, until all the dye has been exhausted from the dyepot - The water will be clear.