I use the cheapest soap (dry and liquid) I can find. I do not have a problem with reusing the grey water in any of my gardens, flower, fruit, or vegetable. I don't think I would have any trouble using grey water that had homemade laundry soaps in it. You use so little of the detergent and a lot of water, so most of the soap is diluted. I do not use grey water that contains ingredients found in commercial body washes, shampoos, or fabric softener. They contain a lanolin-like ingredient that can plug the pores of some plants.