If you are looking to make a slope / bank there are a few different methods that i have seen being usedand used myself...
Method 1: is to literally just keep piling the dirt up into a corner and then slowly plant it, so that the carpet will eventually hold the bank in place over time...
Method 2: get some black stockings (very tight knit type) and cut them into little sections, one cut into small tubes, tie one end off, and fill it with dirt to create a mini sand bag and tie off the other end as wel, create as many as needed and place a long the bottom of the tank, and then lay more dirt over ontop to create large banks / mounds...
Method 3: Get some flexible, but sturdy clear plastic sheets, and cut them into strips (to the legnth you want), and make sure the height of each strip is the height you want the bottom of the bank to be.
Finally, setup the cut strips into the dirt so that its standing up and then keep piling more dirt behind the strip to create the bank leading to the background or something...
Method 4: get a load of rocks for the front of the bank, as well as possibly below the mound / bank, and keep piling them up, once its piled to a height of your liking, lay a bunch behind the rocks ans keep building up the slope...
Hopefully that makese sense, and if not, hit me up and i'll try and explain it better...