True it was found in many ancient cultures.
It surprisingly wasn't mentioned at all in Gilgamesh. And there are several versions of it.
It isn't mentioned in any other Sumerian Literature either
Theres more than one way that several people may die together, To say something like this is gospel and must have happened because it happened somewhere else isn't very good fieldwork. Especially as the news that they found gilgamesh's tomb is two years old and has never been backed up by any evidence since the claim was made is a bit glaring dontcha think

take a look at what they were claiming as Gilgamesh's tomb two years ago again
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Leonard woolley and a few guys from the iraqi antiquities are the only people who've ever dug at ur. Lots of people have been walking out in the desert with handheld magnetometer but they don't find an anomoly and say "aha this must be the tomb of gilgamesh" before they've got their trowel and brush out.
Some people obviously make some very odd claims about the sumerians. They think it's fun and it adds to their ability to sell trashy paperbacks with titles that have "genesis" "eden" or some other loosely related biblical term.
Giovanni Pettinato used to be a respected archaologist and expert on assyrian studies. His astounding new translation of gilgamesh including a completely different ending to all the other versions and has yet to be released. Two years after he claimed to have translated it. what is he a slow writer or something.