Those appear to be your low point drains. directly above them inside there should be 2 valves. If turning them does not stop it then pushs them down gently on top till they snap closed. There are 2 types that are commonly used.
2011- 351RLTS Eagle, MorRyde suspension/pin box,
2017- F350 6.7 PSD Lariat FX4,SRW, SB,CC
Hughes PWD SP-50A, TST TPMS
Gator roll-up bed cover
B&W Turnover ball, Andersen Ultimate 3220
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