Recently I had a plugged drain pipe to my septic tank: plug was within 5 ft of the tank. When I went to use the clean-out plugs to snake the lines, I found that 3 out of the 4 clean-out plugs had leaked big time. Noticed that the caps on the clean-outs were only on finger tight. House was built 8 years ago and have been that way since. (This may explain the slight sewer smell sometimes present in the basement.) End result is ruined carpet. Moral of story; inspect your clean-out caps!
My question is: how to seal these 3 inch caps? Only one of them has an O-ring. The others are just a plastic-on-plastic seal (black PVC or ABS?) with no way to put on an O-ring. Would Teflon tape on the threads do the job? Or if the caps are screwed on very tight, will they still leak? Is there another solution?