You could try baking soda on the iron. Take a damp cloth and sprinkle on the soda and scrub the iron. Then rinse the cloth and wipe off the residue. You will have to do this several times to remove all traces of the soda and don't forget the holes.

When the iron is clean plug it in and run the hot iron over a piece of waxed paoer(protect your ironing board with an old cloth---This will put a light coat of wax on the iron and make it glide smmothly.

I have never left my toilet for months but I imagine a capful of bleach will keep the grungies away.

You can buy the little single use tube of iron cleaner. But why do you think you'll only use it once?

I always sprinkled table salt on a sheet of waxed paper and ran the iron across it several times[hot iron]. If it is really dirty I would use baking soda and water paste to scrub it [cold iron].

If the toilets are definitely going to sit unused for months (i.e. they're at a vacation home or something), you could always turn off the water supply and drain them after cleaning well. Then they should stay as clean as they were when you left them, other than maybe some dust - ha ha!