I have a 2001 Audi A4, and coolant is burning thur the exhaust.  I probably have a head gasket problem and coolant is burning thru.  Very expensive fix and I want to try the Bar's head gasket repair liquid.  I need to drain the system.  I see how to flush it by removing one of the hoses at the resevoir, but dont see a drain valve or anything at the base of the radiator so I cant drian it, which I need to in order to fill with this repair mixture.  Any ideas?

Thanks!    Miked