I would not till or disturb the soil. There are dormant weed and grass seeds in the soil that will sprout if you till. I would like you to realize that the best long term solution is not going to happen overnight. If you plant wildflowers, and do it correctly, it will take about two to three years before it looks like a nice wildflower patch. Patience when working with wildflowers will pay off. Before you plant anything, You will need to kill what is growing there now, so it doesn't out compete your wildflower seeds. I probably would wait until the existing stuff starts not to be dormant....and then spray it with roundup. Round up works while the plants are actively growing, so if they are dormant right now - its not going to do much .... A couple weeks after the roundup application, mow any plant residue left very very short... follow the mowing with light raking to scarify the soil, but don't disturb the soil too much. After mowing and raking, then apply a quality wildflower septic mix from a reputable native plant nursery. Do not buy a can of seeds from a big box retail or hardware store. Reputable native plant nurseries have a pre made mix specifically for septic systems. You may want to roll the seed to get good soil contact but that would be hard on the side slopes. So you can probably skip that part. I would cover the seed, especially on the side slopes with an erosion control blanket like North American Green S150. The blanket gets tacked into the soil and will degrade over time. The blanket will hold the soil on your side slopes until the time that your wildflowers get established. The blanket also acts as a mulch, preventing windborn weed seeds from getting established, and it helps moderate soil moisture and temperature which will help your seeds germinate. You may want to water it a few times. Do not expect any significant growth the first year. In fact I would probably keep it weed wacked to about six inches or so, the first growing seasons to keep anything from going to seed. It helps keep weeds from multiplying and it doesn't hurt the wildflowers. I just use a mower set real high, but it would be hard to do that on a slope. good luck.

When I replaced my septic tank a few years ago, odor from the roof vents suddenly became a problem, which it had never been before. The odor eventually went away, as the tank action got established and a scum layer formed. Until that happened, I was able to temporarily reduce the odor by pouring a few gallons of cheap vegetable oil directly into the tank, to form a temporary layer. Yes, oil in septic systems is generally a no-no, but this was a thin layer, at a level where the outlet tee prevented it from escaping into the leach field.

The tank is not as much of a problem as the drain field. Just remember that if you cover the access into the tank you will be pulling up stones to pump the tank.

Hah, funny Treebird, "wet crappy soil". I have decided to remove the Quercus Alba "rooted acorn" MAYBE,. If I remove the Q. Alba acorn/future tree seedling, I will have no trees RIGHT INFRONT OF MY HOUSE, ON THE SOUTH SIDE. So if I then keep the seedlings I have planted previously where they are, it will be a small wait, perhaps 5 years before the trees I have planted near my house, on the south side, will start to shade some of my house from the southwest to the southeast. To be clear in what I am saying, "I have 2 Compton's oak seedlings, near the eastern exposure of my" house".. On the "Western exposure, there is a " Swamp Chestnut tree" several feet from the Compton's oak seedlings. But, it is best to be able to possibly be able to keep tree tissue and plant regeneration possibilities going straight ahead with the trees I ,have. I am now depending on my 2 " Compton's oak" seedlings. Which eventually will be wanting to "host" some seedlings. As far as my homes southern "light exposure", there are "energies", that can be used by "whatever force" is using our post ideas.