I've tried, but there's not enough power to keep up the pressure.

Difficult to answer... It has power, but depending on how the pipe is laid, it won't work with any compressor. If the cross-section of the pipe is only 80% full (because it is not laid perfectly horizontally), the air will take the path of least resistance, i.e. through the "20%". Perhaps some water will be drawn in due to the draught, but possibly too little. Alternatively, dry out with a hot air dryer on a very low setting. Or lay the hose with a slight gradient and let it end in a depression so that the water can simply run out. Possibly divide into shorter sections, 50 metres is quite long.

Yes, that is certainly possible

The volume is rather low. It constantly tops up the pressure, but this can be tedious. To be on the safe side, I would use one with more volume. But it would certainly work, depending on how long the lines are.