Hi tiddler,
Welcome to the Heartland Owners Forum. There's lots of useful information here along with a great bunch of friendly and helpful people.
The living area slides are probably hydraulic. If you have an electrical failure, you can manually operate the pump with a drill, using a hex bit. I use a 6" phillips head screwdriver bit that's inserted into the drill backwards. You'll also need an allen wrench to manually open and close the valve that allows fluid to flow to and from the slide's hydraulic ram. Some rigs have knobs that you can easily twist to manually operate the valves.
Here's a link to Lippert 0071 which has some pictures along with instructions.
The hydraulic pump and tank are usually located in the front storage compartment. That's where you would add fluid if necessary. If there are no leaks, you probably won't be adding any.