The Man Who Killed Batman - S1-E49
Corrected entry: It's never revealed how Batman saved Sidney from the vat of acid.
Correction: Something not being explained is not a plot hole, nor is it any other kind of mistake. Batman, among many other things, is a ninja and an escape artist. We as the audience understand that he has the capability to rescue Sid the Squid from his predicament, and taking time to explain how he did it would just eat up screen time in what is only a 22-minute episode.
Correction: Sidney is telling his own story and doesn't know how he got saved. He said he must have been sucked down a drainpipe. Later when he finds out Batman saved him, he doesn't ask any follow up questions. The fact that it's never revealed has nothing to do with the plot and it's not a mistake.
Bishop73