mb this in a couple of minutes if fox doesn't want me top educate you without any commercial interest from myself in relation to this very short clip being fairly used by me
There was a place in my city that rented sessions in one. They wanted too much money though :-/
I've read most of John C. Lilly's books in which he talks often about the sensory deprivation tank. I found it interesting that he said never to do LSD in the tank :-P I guess he had a really strong experience there.
I haven't, so I could not really connect to what the guy would say.
The closest experience I have comes when I am in deadline mode and need to work a shitload of hours for several weeks in a row. To cope with that, I start taking naps during the day, of about 20 minutes, up to one hours and a half before the last evening session, and sometimes during those naps my mind gets very clear, and I can do good introspection.