There is no "full draining procedure" for an Epson. Once you get them wet, they're designed to stay that way. You can't really get the heads, dampers, and lines clean enough to not cake up.
My normal way of mothballing a big Epson is to get a chip resetter, an old set of 110ml carts, fill the bladders in the carts with Windex (3 pumps of a 30ml syringe), reset the chips, then print until all nozzles are running clear. Then leave the machine sit with the Windex carts in until she's needed again.
How much for your 7600, and where is she?