We have had mould in our basement near the sewer clean-out for the last 2 summers, this summer being worse than last (we had a wet summer this year). This is a 16 year old house with partly finished basement. The sewer clean-out is located inside an 18 inch square cavity that is cut into the basement floor and the end of the pipe is about 2-3 inches below floor level. The cap on the clean-out is tight and we have had no sewer backups and no reason to suspect anything is wrong with the clean-out piping itself. The cavity is open to the bare ground beneath and has some gravel fill on top (up to the level of the clean-out) and is covered by some plywood. We are assuming the exposure to the bare ground is the issue. My solution is to pull out the gravel and use concrete to create a seal from the bare ground level to about 2-3 inches from the top of the clean-out. Wondering if there are any comments on this or other suggestions?