Fastest peeing relative to their size: cicadas

The #1 animal with the strongest stream of pee relative to their size are cicadas.

By the way, while small animals will produce droplets and larger ones a stream of pee, cicadas are the exception to the rule by behaving like the big ones. This spring, both the 13-year- and the 17-year-brood will surface, so you may get plenty of opportunity to watch them.

Source: https://www.smithsonianmag.com/smart-news/dont-look-up-cicadas-produce-high-speed-jets-of-urine-180983935/

Photo: https://www.pexels.com/photo/extreme-close-up-of-a-cicada-9382342/