[Dancake]

My S40 1.9d also had diesel bug. It never caused any running issues, but I did treat it with expensive marine diesel bug treatment. The tank was always brimmed at each fill, spending more time full than empty due to low mileage and frequent fuel top ups.

Diesel bug grows between diesel and water, so if there's water in your diesel tank then there's a risk of diesel bug developing. Condensation within vehicle fuel tanks and forecourt underground tanks can contribute to water contamination within diesel. I'd be more worried about water than dirt within a diesel tank. This is why you should periodically change your fuel filter or drain the filter bowl two or three times a year to remove any water build up.

I once witnessed a farmer using the nozzle of a diesel pump to poke mud and dirt out from under his wheel arch after he had filled up. The next person to use that pump was at risk of introducing the dirt into their tank. Saying that, I've yet to see a tank on a light vehicle that you could describe as being badly contaminated with dirt. It's mostly heavy vehicles such as trucks, trains and buses that seem to accumulate more debris within their fuel tanks, most likely due to their exposed fillers.