用得當 Aptly Used Indeed
國王笑道：「用得當，用得當。豬長老再飲一杯。」獃子亦不言語，卻也吃了個三寶鍾。國王又遞了沙僧酒，也吃了三杯，卻俱敘坐。国王笑道：「用得当，用得当。猪长老再饮一杯。」呆子亦不言语，却也吃了个三宝钟。国王又递了沙僧酒，也吃了三杯，却俱叙坐。
逐句解 Line by line
The king laughed and said, "Aptly used, aptly used! Let Elder Pig drink another cup."
The king has just had the prescription independently confirmed by his own medical establishment, and his first act is to reward the man who nearly gave it away. 用得當 is verb, particle, result — the light de, and 當 at dàng, apt or fitting. 長 is zhǎng in 長老.
The idiot said nothing further, but drank a Three Jewels cup all the same.
Silenced by drink for the second time in a handful of exchanges, and on both occasions with the thing he wanted in the first place. 子 is the light suffix.
The king passed wine to Sha the monk as well, who also drank three cups, and then they all took their places in order.
敘坐 is to be seated by precedence. All three disciples have now drunk, the vow has been kept by the one person it binds, and the banquet settles into shape.
"Aptly used, aptly used." The king has had the prescription independently confirmed by his own medical establishment and is delighted, and his first act is to reward the man who almost gave it away.
Eight Rules is silenced by drink for the second time in a handful of exchanges, and on both occasions with the very thing he was after. Then Sha the monk gets his three cups, and the party takes its places by precedence. All three disciples have now drunk, the vow has been kept by the one person it binds, and the banquet settles into shape.