Use a wide-tooth comb to straighten out the hair. Make sure no tangles remain in the wig and that it is properly brushed out. This could take some effort if the wig you are washing is very dirty.
Pour cool water into a sink until there is enough water to cover the wig you are washing, and then add synthetic-wig shampoo. Only a capful of shampoo will do the trick - do not add too much.
Submerge the wig in the sink. Allow time for the wig to soak up the water in which it is submerged. While you are waiting for the wig to soak it up, keep swirling the hair through the water with your hand.
When it gets fairly easy to swirl the hair, your wig is nearly clean. Simply drain the sink and wash the wig under cool running water from a tap. You will want to wash the wig until all of the remaining shampoo mixture has been completely removed.
Use a wig comb to brush out the human-hair wig and then rinse the wig under cool running water from a tap.
Apply shampoo formulated for human-hair onto the wig and comb through the hair with your fingers. Once again rinse the wig under cool water.
Dry the wig with a towel until the hair is only lightly damp.
Finally, spray leave-in wig conditioner onto the wig.