We have a smelly toilet problem that seems to have happened after very heavy rainfall about 3 weeks ago. Putting bleach down the pan works for a short while but the smell returns. Where the toilet joins the floor it has a concrete seal around the base, this seems to be damp. 4 months ago we had the drive block paved & the workman put a drain in the drive & connected it to the existing drain system could this be related to the problem even though we have had no problems prior to the heavy rainfall?