After lobbying efforts with Singapore's Ministry of Foreign Affairs, the founding date of WTO was later adopted as World Toilet Day by the United Nations in 2012.

[6] He later enrolled in the Vocational and Industrial Training Board (now the Institute of Technical Education), graduating with a certificate in hotel management.

[13][14] After leaving school, Sim worked as a construction site supervisor and salesperson at Diethelm (now DKSH) before starting a business at 24.

[19] In the late 1990s, Sim watched a speech by then-Prime Minister Goh Chok Tong on the social significance of clean public toilets.

[21] In December 1998, he founded the Restroom Association of Singapore,[22] later launching a rating system for the cleanliness of public toilets in collaboration with the National Environmental Agency.

In his role as director of the WTO, Sim is a lobbyist and coordinator for sanitation efforts,[25] organising an annual World Toilet Summit,[26][27] and contributing to administrative and policy changes in Brazil, China, India, and Singapore.

[40] In 2008, he was appointed to the World Economic Forum's Global Agenda Council for Water Security and the GAC for Social Entrepreneurship.

[28] Sim founded BOP Hub, a non-profit organisation targeting bottom-of-pyramid individuals at the poorest global income margins in 2011,[45] developing a $10,000,000 building in Ubi.

[46] In 2016, the organisation engaged in food relief efforts for migrant workers in Singapore,[47][48] and currently acts as a startup accelerator for social enterprises.