Step 3Hack the Foam
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The foam isn't quite ready yet. You'll need to cut it up a bit to fit on the 1/2" PVC. Take one of the 2.5" pieces of foam. What the plan is here is to cut a wedge in the foam so we can fit it over a 1/2" PVC tee. I used a miter box to help. You'll need to find the slit on the foam, then rotate it a quarter turn and mark the middle. Then you want to draw two lines that form a right angle at the point you marked (see picture). I found it easiest to start the cuts with a utility knife, and make the rest of cut using a serrated kitchen knife. You should end up with a nice 90 degree wedge in the foam. The last step for this piece is to cut through the slit in the foam so it can be opened.
Now you need to modify the remaining two 2.5" pieces of foam so that they fit snugly on 1/2" PVC pipe. Draw a line 1/2" away from the slit on the foam and cut along that. Be sure to cut following the shape of the circle, so the two edges will fit together.