One of the best practices we recommend to our customers is to flush our pump and siphon tools empty of gasoline by draining lines and back flushing with kerosene. Kerosene is a very fine and clean oil that is similar to diesel fuel. You can find it at any home improvement store. In some cases they sell it as reduced odor kerosene which we prefer. It does a great job as a preservative of fuel components. You can simply put the input line and the output line in the same container and flush it through saving it for re-use next time.
Yes, you can use diesel in place of kerosene. When buying kerosene be sure not to buy a kerosene substitute, it does not work well.