Waiver Accountability and Transparency Act This bill imposes requirements related to U.S. Immigration and Customs Enforcement (ICE) granting waivers to immigration detention facilities that do not meet certain standards. ICE shall publicly post within three days of submission each waiver request, request justification, assessment, final decision, and rationale for whether the waiver was granted or denied. ICE shall grade each waiver request from 1 to 3, with 3 being the most serious and including those with issues impacting due process, medical safety, and security. For grade 3 waivers, all parties involved, including ICE, must sign off on a corrective action plan, which shall include a timeline and plan to make the facility compliant with the relevant standards. A waiver may not be approved for longer than 90 days, and waivers may be reapproved every 90 days. After one year, any reapproval shall be approved by the Department of Homeland Security (DHS) and ICE, and DHS and ICE shall jointly publish the justification for the reapproval. ICE shall periodically report to Congress and publicly post online financial penalties imposed on a facility. DHS shall periodically report to Congress and publicly post online an analysis of sample of cases where facility failed to meet a standard but DHS declined to impose a penalty. The Government Accountability Office shall periodically conduct a study on the waiver process and the ability of DHS to hold contractors accountable.