Right now, and in the remaining days before the hackathons convene, the Sanitation Hackathon is soliciting "problem definitions that highlight specific sanitation challenges that could be mitigated by innovative [information and communication technologies]". Examples of already submitted problem definitions include septage management monitoring, interactive applications to promote behaviour change, improving data quality and quantity concerning cesspool/pit water flows, and rapid financial sustainability assessments of sanitation solutions. If you have any ideas, you can submit here (but first you have to register).
To participate in the event, you can register by finding your site and following its unique registration process here. Toilet hackers, based out of NYC, is helping organize the hackathon throughout the United States.