I'm trying to clean and old stainless steel pan which has burnt grease inside and outside. Ideally, the method used should be functional to clean the outer edges of the pan, therefore something a bit stick would be better. How can I do that without scrubbing or using commercial products?
You can often remove crud with electrolysis or lye (drain cleaner, or old fashioned caustic cleaner). I've read about people using a paste made from salt in alcohol or a bit of water for its abrasive qualities.
Electrolysis is accomplished by putting the pan in an electrolyte bath (usually baking soda or washing soda, but I would suggest lye for a dirty pan (wear gloves and goggles!)), and connecting the pan to the negative side of a DC a power source. The other end will be connected to a "sacrificial anode", which is usually a hunk of carbon or non-stainless steel. The current should be a few amps at most. 12-20 V power supplies work well, if they can supply enough power. Take care not to let the anode touch your pot. The pot regions closest to the anode (and in line of sight within the electrolyte bath) will get the cleanest. Let it work for a couple hours, adjusting the position of the anode periodically. If the reaction stops, take the anode out and scrub it. When you are done, shut off power, remove the pan, and scrub it. Electrolysis isn't magic, and the result won't be perfect.
Note that this is a description from memory. Long tutorials and videos have been published on this topic, and I urge you to seek them out before trying it.
You specifically don't want to hear about commercial products, so let me just mention that there are better and cheaper ways to clean your pan. But that would be a different question. :)
Edit: I see you don't want to scrub it, so the only option is to soak in caustic for 24 hours. It won't get all the crud off.
Try putting the pan on a burner and heating it up. Once its hot, some of the grease may liquefy, so the burned on grease may become easier to remove. You can then poke at it with a non-scratchy (plastic) spatula, and/or use a wadded-up paper towel. If you use the paper towel be careful not to burn your fingers!
Removing burned on grease doesn't have to require tiresome scrubbing with abrasives, leaving your pans scratched, nor does it have to require any complex setups or expensive materials. The method described here should only be used for cast iron and stainless steel. It will corrode, damage or stain aluminum.
Visit your local hardware store, grocery store or home center and purchase a bottle of Draino, vinegar, rubber gloves and googles, and a plastic container large enough to fit your pan.
First, put on your protective rubber gloves, goggles and make sure you're wearing long sleeves. Also, make sure you have the bottle of vinegar nearby as you work. Make sure you don't have anything made of aluminum around your work area, as Draino will eat through it. Put the pan in the plastic container and fill it with water until the level reaches about an inch over the highest part of the pan. Remove the pan and pour roughly 1 cup for every 1 gallon of water in the container. Don't be overly concerned about measurement, eyeballing is fine. The amount of Draino to water ratio determines how long it will take to achieve the desired result and how caustic the solution will be. Mix the solution with a piece of wood or plastic for 30 seconds, but don't use a unknown metal object as it can corrode (it could stain or corrode it).
* DO NOT pour water on the Draino as it could react very strongly, causing it to splatter everywhere, including on your skin which will burn you. If you get any Draino on your skin, immediately pour some vinegar on the area.*
Carefully submerge your pot into the Draino solution. Make sure your work area is secured from pets and children. Leave the pan in for 30 minutes to 1 hours and check to see if there's any change. You can do this by carefully lifting the pan out of the solution (wearing your protective gear) and rubbing a small area of the grease stain with your finger. If you notice it smears, wipes off, is soft etc., then you have a choice of leaving it for another hour or calling it done and finish the the rest of the process by scrubbing in a sink. If the stain isn't softened, then leave in the solution longer, checking every hour or so. You can also help the process along by removing the pan and giving moderate scrubbing in the sink and then returning to the solution. If nothing is happening, you may add some more Draino to the solution and stirring it.
When the caked on grease is loose and soft enough to be scrubbed off easily, or no longer visible, take the pan out of the solution and scrub away the soften grease in a sink. To dispose of the waste solution, pour the vinegar into the solution. It may fizz or foam for a little while. When it stops, you can safely dump it down the drain. It doesn't harm the environment as Draino and grease is how soap is made.
While this seems overly complex, it really isn't. The process can take a while, depending on the severity of the stain, but it is highly effective with minimal elbow grease. I stress safety in this process because you're using a caustic chemical which can be hazardous. So long as you're careful and wear protection, it shouldn't be anymore dangerous than using a deep fryer, especially if the Draino is diluted in large amounts of water. Caustic chemicals can feel burn or feel very itchy on the skin and can be neutralized using a mild acid like vinegar. Keep it from getting on your skin and especially your eyes and you should be fine.