I would start keeping a log of all the time you are spending, even just searching like above, in case you file a claim against these perps.I looked at our local tool rental place and they have a few different options for hot pressure washers. One is a 3,500 psi 3.3 GPM with kerosene fired 200F heater. The other is a trailer mounted 3,000 psi 3.9 GPM with kerosene fired 200F water heater OR 225F steam. Would something like one of these work? Is there a professional service out there that might have a way to remove this stuff?