“We are in Seattle, WA. We just completed an emergency repair of our sewer line which is shared with 4 other properties. I have worked out what the shared costs are based on the overall cost per foot repaired and the amount of pipe each of us shares. Can we compel those that benefit from these repairs to pay their fair share of the expense should any of them not want to cooperate?”
You probably can. Many states have laws specifically on this sort of circumstance, and even in the absence of a specific law, it would seem fair that everyone who benefits must contribute to a necessary repair. Hopefully, the courts won’t be necessary, but if it comes to that, keep the option of small claims in mind to keep your expenses down.