Last night I rescued a 7 foot tall bamboo plant but I'm not really green fingered in the slightest and have no idea of how to look after it.

The main tall part of him (he looks like he should be male to me) has a really thick central stem and has lots of nice green leaves.
He has another slightly thinner less leafy shoot and a third one which is all dry and wispy looking.
I think his main root ball is all intact and his soil is pretty moist at the moment, but really I have no idea how much to water him, how often he needs watering, whether I can keep him indoors or whether its best planting him outside (I live in London, so my soil is thick, clay and gets waterlogged very easily), what kinda soil he'd need, and how best to trim him down to a more reasonable height.

Help me! (And Brutus!)