Three times oyster content gets sent back in US national park (8)
I believe the answer is:
yosemite
'us national park' is the definition.
(I've seen this before)
'three times oyster content gets sent back' is the wordplay.
'gets' indicates the answer is hidden within the clue.
'sent back' is a reversal indicator.
'etimesoy' can be found hidden inside 'three times oyster content'.
'etimesoy' in reverse letter order is 'YOSEMITE'.
'in' acts as a link.
(Other definitions for yosemite that I've seen before include "Where there are watery cascades" , "US National Park in California" , "Natl. Park in California" , "Californian national park" , "California falls, valley, park" .)