How long it takes depends on how hard you want it. /forums/images/graemlins/grin.gif
You can roll it and then cross roll it to get it beat down but it all depends on what you want. A 3 ton machine might be a little overkill so one pass would probably be ok, but it depends on what you want and how rough it is to start. Most of those rollers can move out pretty well when you crack the throttle so time wise depends on how much open area you can cover. Just take it easy on the fwd/rev levers at the ends of the passes, ease up early and change directions slowly, and take it slow until you get the hang of it. Dont turn sharp, take it in little changes on each pass. Use very little direction control, a little bit at each end will put your wheels on new dirt using long passes.
The leach bed should be ok the pressure would be spread by the earth and the pipe is surrounded, I was just worried about the concrete on top of the tank. If it is perfect, then there would be no problem. If its flawed, then you might end up with a roller in @#$% soup, or ruin your lid.
Terrain wise, well, I wouldnt put a roller on my back yard, yard being used loosly here, but the front no problem. Its probably a 1' to 10' rise or a little steeper. Cross rolling that wouldnt be a problem. Up and down the slope is really only limited by traction.
Hope this makes sense to you. Just like any other piece of equipment there is a learning curve. Start in a flat area till you get the hang of it.