Being to the negative end of the Domestic Godddess spectrum, I've never invented a household hack before, but it's never too late so here goes:
I have been using cake shampoo for sometime to avoid plastic waste, but am infuriated by its tendency to stick to everything, fall apart, and disappear down the plughole. Now I break it up, stuff it through the neck of a used plastic shampoo bottle, add some water and shake like mad in time to the song I'm singing. Result.
For those who are concerned, I ONLY sing in the shower.