When Rocky is just finished with "Sword of Damocles", he is climbing back into the gene pool. From the side you still see the stripes of color, yet from the top you can see it is completely empty.
The pool is also empty when he stands up whilst still wrapped in bandages. We can only assume the water is absorbed into him as he is 'born' (although I admit it's a lot of water'.
Plus, it'd make a mess....
Ah, yes. But did you notice that even though the liquid has drained from the gene pool, that all rocky+'s bandages and even the material at the bottom of the tank are all bone dry!!!!
Just like Huga and Cher said, the tank is empty when Rocky goes to get up, and is bone dry when he gets out
After just watching, I noticed that it starts out full of water, then they cut to Riff-Raff (who shuts something off), then they cut to the light above Rocky's tank, when they cut back to Rocky's tank, you can tell that it's empty