The fuel tank sealer comes in a kit, called a Fuel Tank Resto Kit. It contains the POR cleaner "Marine Clean", a metal etchant and rust remover "Metal Ready" and the "US Standard Fuel Tank Sealer". The sealer is much thicker than water, but you do need to plug all the holes, inlet pipes etc, except the one you use to pour the stuff in through. They claim that it will seal small pin holes. The kit cost $99 +p&h, but it will do at least two VW size tanks.
The Marine Clean is one of the best wax & grease removers I have ever used, much better than any of the solvent based ones and it can be reused many times. The Metal Ready is also a top rust remover and preprimer, it can also be reused many times.
For all the info and local resellers see the website
www.ppc.au.com