There are many ways to remove grease from a surface which is what you are doing , irrespective if its an oven or not.
The most common use of a tank system in vans is to clean grease filters from commercial kitchens. They nomally use crystals which you can buy from a number of places.
However the commercial guys often get them from Fans & Spares, who have branches up and down the country, no doubt there will be other companies with their own version.
To be honest if you clean in situ, your hard pushed to beat the domestic cleaners, the key is to use a foam to suspend the chemical long enough to work.
I used to use a chemical called F1 (5lt) which was ok in cold water however I then tried it in very hot water and it improved it by 500%, never found anything to beat it commercialy.