Yuri starts at page 15, where Tenryuu asks Naka to become her girl (read: assistant), examines her shipgirl cavities (diagnoses an oil leakage and recommends that she be more serious about maintenance) and her finger hits fly ash (read: shit), after which she instructs her to release all of it over her body (female on female shit on vagina/女同士でマンコに塗糞/糞まみれ). Naka gets shocked at Tenryuu's fuel tank getting hit by her burning fly ash (while releasing her drainage liquid - female on female urination/golden shower/女同士で浴尿), after which Tenryuu proceeds to perform drainage inspection (as it's part of the maintenance process, right?!) - and asks for another cup of drainage liquid. Yuri closing on pages 19-20 with Kongou joining them and asking for a drink as well.
Shame that more artists don't take similiar approach to keep yuri and het completely seperate if they want to put both in the same work using different characters, it makes deleting unwanted content more simple and keeping remaining thing pure to their own liked fetish.