- 1). Press non-hardening clay into the bottom of a small cardboard box. Hollow out a mold from the clay, leaving a vertical void the size and shape of the coupling.
- 2). Apply a light misting of mold release spray, holding the can 12 to 16 inches from the clay.
- 3). Mix the silicone or RTV compound with the catalyst in equal parts.
- 4). Pour the rubber into the hollow area in the clay, and fill it to the top of the mold. Do not over fill and allow the rubber to run from the mold.
- 5). Allow to cure for 24 hours.
- 6). Peel away the box. Press the clay out from the sides of the coupling, and pull the rubber from the clay.
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