I'm with spek, depending on the soap you use it could mix into a toxic solution that will straight kill your girls. I dodged that bullet. The last time I fully washed my girls' bins, I guess I didn't rinse them well enough and there was residual soap left inside them, and their solution got frothy. They were in that solution for 2 days. They got a bit burned before I could re-rinse them. I use dawn, it has no phosphate, but still burned my girls a little. No soap in the res, or nutes. Foliar only.