I'm putting sheet vinyl onto concrete in a small 3/4 basement bathroom. When I pulled up the carpet squares, there is a patch where the previous owner connected the shower drain to the main sewer line. It's only about a square foot, but one edge was not smoothed out very well and there is a bump about 1/8" - 3/16" high right there. If I put down the sheet vinyl I'm sure I'm going to see that bump. Short of pouring levelling concrete over the entire floor, is there any way to level it out, such as grinding down that little area? If so, can you recommend techniques and tools?