Step 3: Microwave it.
Put your microwave on for maybe 30 seconds.
!!!WARNING: WATCH THE SOAP VERY CLOSELY, AS SOON AS YOU SEE ANYTHING RISE OUT OF THE CUP, TURN YOUR MICROWAVE OFF!!!
After you've microwaved the soap until some of the water rises out of the cup, remove it from the microwave and set it somewhere. You can use this time to find something that has the same diameter as the middle of the cup, and a sandwhich bag or ziploc bag. Put the object in the bag, (I used a vitamin bottle) and push it into the soap to make it more dense.