Getting same water purifier issue as OP. Pipes are full with contaminated water going in and clean water going out correctly since it was working before. Have rebuilt the purifier unit, the wires & pipes. Dupes still not sending sand even though I have increased priority to 9. This has happened in new words as well. I notice it works at first then stops around cycle 68. I am on cycle 190 right now and dupes still ignore delivering sand.