Coulant drain plug location in Fiat Ducato engine block?

I am changing the radiator in my 2.5 D May 1997 Ducato and want to take the opportunity of flushing the cooling system before refilling with fresh anti freeze. the Peter Dussek manual says simply "remove the protective panel below the engine and unscrew the plug in the cylinder block...". Can anyone tell me what I should be looking for and where?