Once you've completed the quest to kill the oversized slug-thing that is Duriel, the correct Tal Rasha tomb symbol no longer shows up in your quest log. How do you find him to kill him again? Is there an easier way than going into all 7 tombs?
If you created the game and still remember the symbol, it shouldn't have changed. Otherwise, the symbols on in the Summoner's chamber in the Arcane Sanctuary show the false tombs. The one symbol that doesn't appear there is the true tomb.
The 3 prime evils (also NM Andariel and Pindleskin) are better choices for boss farming as they drop better loot.
Unless you're dead-set on exploring all seven tombs, here's one method I use:
I start from the rightmost tomb, head left until I find the correct tomb, and then go in, ignoring any other tombs.
Then the leftmost tomb on the map will always be the correct tomb, because tombs further left won't show up on the map.