Let's clarify some points.
First of all, yes, even TONMO.com people have kept bimacs in 30 gallon tanks. That was before we realized that they needed more room and some of them would grow large enough to require the 50 gallons as a minimum. Most octo keepers want to provide room to explore and play, so we find many putting bimacs and similar-sized octopuses in even larger tanks. What we're aiming at is "good animal husbandry", not the minimum we can get by with.
Secondly, how big is a tissue box? I guess I haven't bought tissue for years, but boxes were various sizes, and yes, Ollie would have fit in some of them.
Thirdly, you say you kept a bimac for almost 3 1/2 years. This baffles me, since the longest lifespan I've heard of (and not verified) up till now is 1 1/2 years, in a lab somewhere. Bimacs are a few months old when their owners get them, and it's an accomplishment to have them live with you for 10 or 11 months. Over three years is getting into the lifespan of a Giant Pacific Octopus, not a bimac. There must be some confusion about the species or about the lifespan.
Nancy