Here it is with the top cut off. I also before this had sliced a little off the bottom so it would stand up better. I used this to cut the top off. I really have no idea what it is normally for--the only thing I can ever remember using it for is carving pumpkins.
Next I scooped out the inside of the watermelon. I had originally planned on using a melon baller to make it nice and pretty but soon realized that to do so would take me approximately forever. So instead I used an ice cream spade. It was not nearly as pretty but once we cut up the scooped watermelon, you could hardly tell.
After it was sufficiently scooped out, I used an apple corer (which happened to be just the right size for our spigot, but you should check first) to cut the hole for the spigot. We put it fairly low on the watermelon for maximum fountain potential and it worked quite well. You'll just kind of have to guess though as to where to put it, based on our watermelon, spigot and where you plan to serve it.
Here's the almost finished project still in the kitchen. As you can probably tell, it made a bit of a mess, so plan accordingly. For the watermelon lemonade, we did things a bit differently. We weren't sure how long the watermelon fountain would hold up and we were going to serve watermelon anyway, so mom got a second watermelon and cut it up to make the puree. She strained it then froze part of it in a tupperware container to keep the lemonade cold then put the rest in the fridge. We broke the frozen part into a small enough piece to get it in the watermelon then mixed some of the puree with lemonade (she likes to use some frozen concentrate with a tub of the cheap Crystal Light type mix). We ended up with enough ice and lemonade to fill the watermelon twice. Here is the finished product out on the table:
We put the tray underneath it in case it leaked. The lemonade didn't come out superfast, which was ok. We did have one issue with it getting clogged, but it took me all of five minutes to get it taken care of. It was a huge hit and everyone loved it!