Once again on PD3: "3. The magnitude of pleasure reaches its limit in the removal of all pain. When such pleasure is present, so long as it is uninterrupted, there is no pain either of body or of mind or of both together."
It seems to me that the second sentence in particular, and in fact PD3 as a whole, are generally considered to be hard to understand. That is probably a factor in why there is a temptation to abbreviate it as "what's good is easy to get" which may be true but seems off from the point in issue.
But consider whether this excerpt from Gorgias may explain the point in issue:
SOCRATES: There is pleasure in drinking?
SOCRATES: When you are thirsty?
SOCRATES: And in pain?
SOCRATES: Do you see the inference:—that pleasure and pain are simultaneous, when you say that being thirsty, you drink? For are they not simultaneous, and do they not affect at the same time the same part, whether of the soul or the body?—which of them is affected cannot be supposed to be of any consequence: Is not this true?
CALLICLES: It is.
SOCRATES: You said also, that no man could have good and evil fortune at the same time?
CALLICLES: Yes, I did.
SOCRATES: But you admitted, that when in pain a man might also have pleasure?
SOCRATES: Then pleasure is not the same as good fortune, or pain the same as evil fortune, and therefore the good is not the same as the pleasant....
Referring back to PD3, does not "when such pleasure is present...there is no pain...." explicitly answer Socrates objection by pointing out when the vessel is full of pleasure, and all pain has been ejected, pleasure and pain are at that point NOT simultaneous?
And does this not explain and constitute an explicit statement that the highest good is to have the vessel totally filled with pleasure and completely emptied of pain, because at that point the experience is totally pure and unadulterated, which is a requirement for anything to be considered the highest good?
Cassius Amicus I suppose one can be VERY thirsty, and drink a little, still want a lot more. Socrates will use that to say that the person is both thirsty and feeling relief at the same time, and that because he has set up a series of definitions that says good and bad cannot coexist as a mixture, the pleasure of drinking (and pleasure itself) cannot be "the good."' So the issue of how to respond to these dialectal games is unfortunately important.