If the foam float in your rain gauge measurement tube has deteriorated, you need to replace it with fresh foam. Use a broomstick to pop the old foam out. Discard the old foam.

To prepare the new foam, run a bead of silicone around the inside of the blue tube. It doesn't have to be pretty—you're going to smooth it out with the toothpick. Using the toothpick, swirl the glue around the inside of the tube, creating an even coating about 2 inches into the tube. Take the new foam and use a twisting, pushing action to press it inside the tube. It's not the easiest job in the world—you need a bit of finger strength for this job. Press the foam in so that it's just even with the bottom of the blue tube. If you push it in to far, reach for the trusty broomstick to back the foam out to even. If any glue got on the outside of the tube, wait for it to dry before putting the tube back into the copper flute.