This is not just a toy, it's the most crazy product ever! - run a shallow bath and sprinkle in the dry powder over the surface of the water, the whole lot turns into a brightly coloured sloppy, slimy, gel. We ran a bath of 6cms as instructed, and it was a fairly 'firm' gel, so could have been a bit deeper. It is like the gel which retains water for plants or flowers. My 9 yr old got in and so did the 13 yrs old who both spent the next 45 minutes playing in it. True the bathroom got covered in a fair bit of it, but it just wipes off and doesn't seem to stain anything. Also if it slops over the side of the bath it stays as a small lump, so doesn't flood the place.
As they say this would also be a great outdoor summer paddling pool product. When you are finished, just add the other packet it comes with, which it turns it into a more liquid product, and hence will go down the plughole easily. Don't worry I don't think it would block a drain as it feels like lots of small particles once it is made up, it's not like a jelly, all solid. My kids are now desperate for some more!