How to Make a Watermelon Keg
To make a watermelon keg, start by cutting the top off of a watermelon and scooping out all of the watermelon flesh on the inside of the fruit. Then, wipe down the inside of the hollowed watermelon with a damp paper towel to get rid of any seeds and residue. Next, start by making a hole near the bottom of the watermelon that's big enough for a spigot line to fit into it but small enough that there won't be a gap. Finally, insert a spigot into the hole, fill the watermelon with some punch, and use the spigot to pour your drinks.
Wash the watermelon. Scrub it well and pat dry. Make sure the surface is clean and free of any dirt, so it will be ready for decoration and carving. Mark the cut line. Draw a circle around the circumference of one end of the watermelon where you'll remove the top. You may want to use a drawing compass for accuracy, or simply sketch as neat a line as possible. Draw decorative features. Mark parts of the watermelon using a pencil or a Sharpie. You will most likely fill the watermelon with punch three-quarters of the way, so if you want to carve any decorative shapes or designs toward the top, map out the design now. Cut off the top of the watermelon. You'll need the top as a lid that goes back on the melon after you've added the punch. Use your sharpest kitchen knife or a box cutter to slice cleanly through the melon. Follow the pre-drawn lines when cutting; this will make it easier. Gently remove the top. Clean it of any residual watermelon, and then set it aside. Scoop out the watermelon flesh. Lay down newspaper or sheeting underneath the watermelon—this is going to get messy! You could also place the watermelon in a deep sink to reduce mess. Just like carving a pumpkin—only wetter—scoop out as much flesh as possible with an ice cream scoop or large spoon. When scraping out the flesh, take care not to scrape too much of the skin. The idea is to hollow out the watermelon neatly without creating indentations in the outer edge. Save the goodies. Try to remove the watermelon in chunks so you can use the fruit later either in your punch or as a snack. Clean out the inside of the watermelon using a wet paper towel. Remove any errant seeds or pieces. You should be left with a smooth, hollow surface. Create the “watermelon keg”. Make a hole toward the bottom portion of the watermelon using an apple corer. A hole approximately two to three inches (5 to 7.5cm) from the base of the watermelon is appropriate. Then when the watermelon sits on a table, guests can easily place their glass underneath the spigot. Make the keg hole the same size as the spigot line. You will want to fit the spigot snugly into the hole created by the corer, but not so large that a gap is created. If the spigot line has a sharp edge and the watermelon skin is not overly tough, try puncturing the skin using the spigot and bypass using the apple corer. You may find that you get a tighter fit this way. Fill the fruit keg with your favorite punch recipe. A punch recipe that infuses watermelon or watermelon flavors would be most desirable, but any punch recipe will work. Test first! Pour only a few cups of the mixture into the watermelon to determine if the spigot will leak. If it has a leak, fill the gaps with either pieces of rind or even duct tape around the inside the spigot line, inside the watermelon. Hold the duct tape in place with pins if it does not adhere to the watermelon (which it very well may not given the wet and slippery surface). Add watermelon. Integrate pieces of watermelon flesh into your brew when preparing it. This will further enhance the flavor and taste. If possible, re-use the chunks of watermelon in your punch and float several pieces inside the punch for good visual effect. Place the watermelon keg on display. Decorate the watermelon using other pieces of fruit. For example, you could create a fun face using apple pieces, dried fruit, and watermelon chunks. Affix fruit pieces to the watermelon using toothpicks. 
Wash the watermelon. Mark the cut line. Draw decorative features. Cut off the top of the watermelon. Gently remove the top. Scoop out the watermelon flesh. Save the goodies. Clean out the inside of the watermelon using a wet paper towel. Create the “watermelon keg”. Fill the fruit keg with your favorite punch recipe. Test first! Add watermelon. Place the watermelon keg on display. 