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Its going to be tough to get an unwilling octopus out of its tank. It has hundreds of suckers and immense strength, getting him out is going to be difficult. You could ask for advice from the place where you acquired your bimac.
I was thinking about this problem, and if you can engineer a box with a lid, put some food in it, then some how have the lid close with a string when the octo gets in it. I think it will work, but maybe not