The Sea
The Sea
[Cueball stands on a beach at night, staring out across the moonlit ocean. The three lines of text stand above the moon, above Cueball (white on black), and on the beach (black on white).] Cueball: The sea always makes me realize Cueball: how small I really am. Cueball: I should get one of those pumps.

Cueball becomes introspective when contemplating the sea. The straightforward reading of "how small I really am" means he feels humbled by the sea and recognizes his insignificance on this planet. This is a common sentiment expressed in poetry, literature, and blogs.
The final line I should get one of those pumps is most likely to, at first, be understood as getting a pump to drain the ocean. The reflection on the joke would run along the line that Cueball is so unsatisfied with the way the ocean makes him feel, the size of the sea intimidating him, that he intends to drain the sea to make him feel better about himself. (This is of course impossible as the size of the sea is many billions if not trillions of times bigger than the biggest storage tanks on Earth today.)
However, in English, the sentences I'm small and I'm big can also be a euphemism for my penis is small and my penis is big .
Even if Cueball is not literally saying that he has a small penis, men very commonly associate their own self-image with the size of their organ. Therefore, enlarging it would improve their self-image and make them feel less small.
The final line in the comic: I should get one of those pumps , could thus be understood to reference a penis pump , a device that is alleged to permanently increase the size of the male member.
The title text is referencing that Cueball would also like another pump - and this one should be the one for draining the sea. But by specifying in the title text that the first pump is not for the sea, Randall is ensuring that it is possible to understand the full joke.
[Cueball stands on a beach at night, staring out across the moonlit ocean. The three lines of text stand above the moon, above Cueball (white on black), and on the beach (black on white).] Cueball: The sea always makes me realize Cueball: how small I really am. Cueball: I should get one of those pumps.
