The pair claimed a silver medal in the opening FINA World Series event in Beijing, China.
Couch and Leeds teenager Toulson were only beaten by home favourites Huixia Liu and Yajie Si in the women’s platform synchro competition.
The Chinese pair scored 334.68 points, with the British duo collecting 317.46. Malaysia’s Yee Mun Leong and Pandela Rinong Pamg were third with 311.70.
Last month, Couch and her regular partner Sarah Barrow won a World Cup bronze medal in Brazil to secure Great Britain one of just eight synchro Olympic places.
Meanwhile, there was also success for Tom Daley and Plymouth Diving’s Dan Goodfellow in the men’s platform event in Beijing.
Following on from their bronze at the World Cup on their international debut, Daley and Goodfellow claimed another third place with a score of 420.15 points.
China’s Yue Lin and Aisen Chen won in 477.15 points, with Ukraine’s Maksyn Dolsov and Oleksandr Gorshkovozov second with 426.21 points.
Couch and Daley will dive in the individual platform events on Sunday.