If the slope is that steep and you cant manage to haul water down there, just set up a 10 gallon reservoir near your plants with a green garden hose running from the reservoir up the slope, possibly hidden with leaves. You can rig up some kind of funnel very easy at the top, keep it small, enough to pour 5 gallon buckets of water through it. So my theory is you can haul two five gallon buckets of water to the top of the slope, pour it through the funnel, down the hose right to the reservoir at the bottom, saving you the painful progress of walking down the slope with heavy water. One thing is key, and that is growing on southern slopes, marijuana enjoys being planted on southern slopes, because of maximum sun exposure. One factor that does come into play with slopes is when there is a lot of rain, erosion can happen, washing the plants away. But growing on a slope can also play in your advantage, you can set up irrigation channels in the soil making the water running down hill direct to your plants. I have grown in slopes before, and I will dig away at the bank, giving me more of a flat area to have a nice area to plant. An alternative option would be to grow in pots, you could strategically place 5 gallon buckets all along the the steep slope, simply burying the bottom 6-12 inches of the bucket. I hope that helps, happy growing