idiot of the century

I love my Freelander 3 door TD4 sport 2004.
and today I put 50 ltrs of prime 97 Octane into the tank and drove off.
1 mile down the road and a couple of kangaroo hops later ...my brain woke up ....switched the engine off and arranged a tow home.
now I know I have to drain the tank....but the question begs.......HOW?

is there anyone out there willing to help?

ive answered yer in yer other post

Thanks,
I think you can tell I'm new to this.