So me and the girl are gonna have some fun in some gunge next weekend that I ordered
from messy supplies. We plan on filling a pool with it. What would you guys recommend for
mixing? Is just using your hands to mix ok or is there something easier? What about measuring out the correct amount of water? It's thick MS gunge.

Bucket at a time. Warm water, add the powder and mix. I use just a hand whisk and it takes just 3 mins to make per bucket. Just make sure you've broken down all lumps before you stop mixing. Use a 14L bucket and fill to about 2 inches from the top.