Step 5: Finishing touches
I bought 3 different sizes of foam pipe insulation (1/2", 3/4", 1"), cut them into pieces 1 to 2 inches long, then painted all those pieces bright yellow.
With all the bits sorted by size, I began gluing these to the underside of the tentacles with liquid nails. Larger diameter pieces went toward the sewer, and smaller toward the ends. I think I used around 250-300 pieces. It's impossible to get this wrong and the extra detail is impressive!
The last steps involved mounting the manhole cover in the grasp of one of the tentacles, setting up a couple spotlights, and the addition of a fog machine. A small fog machine sits in the shorter, lower tentacle and faces toward the sewer opening. A timer dispenses occasional bursts of fog which emanates from the base of the tentacles like sewer steam, or maybe smoke from the ruckus below. Since the tentacle itself is a duct it's perfectly suited to carrying fog from point A to B.
Safety Note: Before placing a fog machine in a confined area, review how hot its surfaces become in use, and situate it so nothing is making contact with a hot surface.