Slide out/Bump out what's the poo?

With Schwintek slides, there is an electrical override. If that fails, remove the motors and push really hard.

The fail safe on mine is a valve to completely release the hydraulic flow back to the reservoir and a hand crank winch like you’d find on a boat trailer, you just winch the slide back in, not much work at all, but slow.

Both of the 5th wheels we had didn't have a strictly manual way of opening the slides. They were hydraulic and the manual way of opening them, was to bypass the electric motor and use a drill to turn the hydraulic pump, thus opening the slides. This was as "manual" as it got, and the way recommended by the manual.

I suppose you might be able to crawl underneath and try to turn the shaft by hand, but I have no idea if that is feasible.

As said, most do have a manual override of some sort, depending on the slide mechanism. Our coach for instance, came with a long crank that's fitted through a small opening where it engages with the drive motor/gear box assembly to retract the slide if needed. I've tested it, and while it does give your shoulders a workout, it will get the job done.

Yes, most if not all slide out rooms have a way to operate them manually...
Depends on the make. The manual will detail the procedure.