No one has poured anything weird down it (separate bathroom for DH and I, so no kids involved). The bath is not new. We are not using any new products. But since midnight Friday night there is an overwhelming smell of petrol in the bathroom and it is coming from the bath plug hole. Nothing coming from the basin (strangely - as the pipes do join up) - so it has to be the bath plug hole or pipes. We have had the thing entirely dismantled and cleaned with bleach/vinegar/bicarb. Smell goes away for a while, then comes back. Pleeeeeease? Anyone? I am dying here!!