i'm going way out on a limb here. i've only worked on two hydros, but only as it pertains to contruction. it would seems to me as it refers to all the crap that comes out of the out-take pipe.
I guess 'bought out' means off-the-shelf from a distributor, rather that obtained from a manufacturer (possibly to custom specification, and after a tendering process etc.).
Can you ask whoever authored whatever it it you're reading?
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"Love justice, you who rule the world" - Dante Alighieri
The BOUGHT OUT ITEM REFERS TO THE COMPONENT PURCHASED AND FITTED by the MaiN Supplier to whom order is given, and that supplier is not doing the component in his own works, but the main responsibility lies with the main supplier, who has taken the order.