Cant find the link, but a site I saw recently used the milliput by rolling it out flat, the marking it, the cutting it into the appropriate sections.

My own was much simpler and was cheap and effective too, I spread cheap 'no nails' type adhesive onto the tank and did the marking with a small section of a comb of all things!
Use a fine toothed section and wipe the tool after every wipe, it goes much faster than you would think. You can also 'detail' it very easily by picking sections away, they seem to just the way you want, leaving a very nice worn flaked off effect.

I did a bit of research into the zimmerit and its application, it was pretty simple stuff and was applied in two layers, the first being in squares the second done later in the wavy lines pattern with either a roller or small rake like tool. My damged zimm has bare steal patches, perhaps it should be squared???

BTW...my 'no nails' came from a pound shop, if your UK and get stuck I'll send you one.