Sounds like the neighbors kids did you in. Pull the cap and look down inside if it looks like the pipe sweeps toward the street, then it is probably a clean out. You are probably best off to get a pro in to flush the line. Make sure the cap is tightened afterwards.OK, I have a question to see what I need to do and to confirm what I have. I live in a townhome and there is a sewer cleanout in our from walk from the sidewalk to the door. This is a 4" cleanout with a drain cover on it. This morning after taking a shower I noticed the sidewalk wet around it and some paper debris around it. From seeing this I thought there was a backup and confirmed it when I ran the kitchen faucet to test and saw water flowing out. I'm assuming this could explain a rotten egg smell I recently noticed from the washer and the dishwasher as well. Not too long ago I found the drain cover loose and discovered neighbor kids putting rocks and other debris down it. I screwed the cover back on but we now have this problem. Am I correct in thinking it's backing up from the debris dropped down there or could I have another problem? Any ideas of what I should do or do I need to call RotoRooter and bite the cost?