Why start a thread? No offence, but I read the original post as you were arranging one.
There's and annual meet up around spring time each year, it was in Liverpool this year. There's a London meet and another in Bristol, but I'm unsure when these are. In September there's a Midland meet. Why don't you go to one of them?
If you're gonna have a piss up in a drain or underground site, I wouldn't arrange it like this. Do it more privately. But when you've got a date and location, remember to send me an invite
I think it's a good idea to wear a life jacket any time you plan to get pissed. Look at all those people who fall into the Irwell or MSC after a night out.