A Hot Wet Job for Three: Adult Toy Tester

Mutsumi, a poor college student, takes on a shady but well-paying job as a toy tester, only to find out that the toys in question are exclusively for adults! His employers are a pair of handsome studs from his college, Kamishiro and Takase. Despite it being Mutsumi's first time, they test all sorts of toys on him, in various situations...

(Source: Renta!)

Note: Contains four extra chapters.