How can we level out a mound in our backyard?

The mound is due to the soil being disrupted, unless there was something put in with the pipe like gravel. The soil will need to be compacted by either a human or Mother Nature

I would leave for a year an then resold .

The neighbor directly across from me had that done and her house sits back and it left a slight depression eventually in the middle of her yard. I’m getting ready to have mine ripped open anytime now. I dread the thought but in a way its good for the soil to be aerated a bit & maybe my lawn will begin to improve.🐸

At least 4 - 6 months and that would depend on how much rain you've already had. If you've had a lot then it's probably done settling and if you level by hand with a shovel you can decrease the height by taking the additional dirt and spreading it out around the base till it all blends. We recently had new septics put in and the mess was horrible, they waited 6 months to clean up their mess.

Mr. Tom, If gravel was added, it displaced the soil. Think of emptying a bucket of soil, then add a few inches of gravel and try to put all the soil back in. Some may go down, working it’s way between the gravel, a good portion won’t. Too bad the plumber didn’t take the time to level it some. The mound will not go down to the original level. A tractor would be easiest to regrade, but you could do it with a wheelbarrow, a grub hoe, a flat shovel, and a garden rake. Do you have any low points in your yard to put the extra soil?

Tom, the gravel took the place of the soil (displaced). The mound will not settle fully. Think of having a bucket of soil that you dump out and put a couple inches of gravel in. Then try to replace all the soil you dumped out. There’s not enough room for all the soil you removed. You will need to do one of two things, use a tractor to level and spread it, or use hand tools. At my age and health, I’d get a tractor with a scraper attachment to get it to just a wee mound and then use those chain link levelers that ride behind the tractor or riding mower. We used the truck in the area a when I was a kid. By hand, and depending on length of mound, a grub hoe, garden rake, flat shovel, wheelbarrow and find a spot for the soil. The folks who dug it up could perhaps fix it. You will of course need to reseed and lay straw. If you have no low lying areas in your yard, you can think of adding the soil to a raised bed, raised garden, possible water feature or have it hauled away.