Otic suspensions have a positive effect on the duration of otorrhea in children with a tympanostomy tube. It is still questionable how eardrops reach the middle ear. We hypothesized that otic suspensions do not pass the tympanostomy tube if the middle ear is dry but pass by diffusion when wet. The median concentration of Evans blue (colorant) in the middle ear was <15.6 mg/mL (lower limit of quantification) when diffusion was impossible but 45.3 µg/mL when diffusion was possible (P = .01). When the outward flow was increased to 0.1 mL/h, the concentration of Evans blue in the middle ear increased significantly (P = .03). With further-increasing outward flows, the concentration of Evans blue decreased linearly (β = −144, P < .001, R2 = 0.44). We conclude that diffusion is the mechanism by which otic suspensions enter the middle ear in children with tympanostomy tubes and otorrhea.