Rod made a good point. Are you certain that this is exhaust residue and not residue being washed out the drain holes from a manufacturing process? The “sniffer” would at least confirm or disprove exhaust as the source.
By the way, manufacturing residue coming out the drainholes would not be acceptable, but at least it wouldn’t be dangerous. Stamping oils, welding residues, they can both be messy but not dangerous.