So I've been thinking about this for a couple hours now, and I'm curious if my solution would work...was wondering what you think of it.
So the casing was a sandwich of (from outside to inside): steel, conductive foil, rubber, conductive foil. The inner foil cannot touch or be electrically bridged to the outer foil or steel case without completing the circuit and detonating it. Also you can't vibrate it too much or the tilt sensor will trip, and you cant flood it because of the toilet float trip.
So that got me thinking...what if you were to gently remove the paint and oxide layer off the steel case and apply mercury. This would over the course of a few hours form a very weak amalgam with the steel (softening it considerably). Then use a file or something abrasive to VERY SLOWLY (using a minimal amount of force to make contact with the metal) scrape away first the steel casing, then the foil, then the rubber, and finally the inner foil; making sure to clean the point of entry after each layer to prevent the circuit from being completed. In theory if you did this slow enough, with a small enough force, it shouldn't vibrate the machine enough to swing the pendulum/tilt sensor.
So now that you are inside, you could use one of those flexible wire type cameras to have a look at the circuitry/mechanisms. Or you could disable the float trip by inserting many small lead weights connected by a string to weigh it down; or you could cut a large hole in the float so that it floods.
Finally, you would flood the case with ferric chloride, which will quickly dissolve (a couple hours tops) any copper wire and/or printed circuit boards...thus disabling the entire mechanism. You may have to replace the ferric chloride a couple times depending on how much copper you dissolve with it.
What do you think? Would it work?
Here is a quick source about weakening stainless steel with murcury: