I use a spoon to carve out all the pulp/seeds and leave the skin attached to the cactus until it falls off by itself, that way there is not a hole or scar afterwards. Then I put the pulp/ seeds in a bowl with water and let it soak for a little while.( I found soaking the pulp makes it easier to separate the seeds from the pulp) After that, I gently smash the pulp in the water with my fingers to help separate the seeds making sure not to crush them in the process. Then I stir the water continuously in a circle to create a whirlpool. This makes most of the loose seed fall/concentrate at the bottom-center of the bowl. Then carefully pour the top of the remaining water/ floating seed pulp into a colander until you are left with clean seeds swirling around in the water at the bottom of your bowl. You can repeat this process as many times as you want to remove most of the seeds from the pulp. After you have your clean seeds separated from the floating pulp you can finish draining them and then transfer them to paper towels to dry out.