My betta actually lets himself get suctioned to the filter. It's not a very strong filter so he can get away very easily. I was so scared the first time he did it. I went in there with the net and before I even got near him he'd detached himself and come up for food. The next time he did it I was still a bit scared, but I did the net thing again and he swam right away from it. He also likes to ride the small current the filter lets out. His fins never get sucked into the filter, he just sticks his body to the side for a nice little massage. He also swims in the leaves under the filter so they move as he goes through them. It's so funny!