The tropical species of octopus (such as O. briareus should be kept at higher temperatures. We usually say 76-78 degrees, but probably up to 80 would be OK. The bimac is not a tropical octopus and needs lower temperatures.
You'll find many posts about using duct tape to seal the top and prevent escape. Be sure also to read the Equipment List, which you'll find by pressing the Ceph Care button above.