Justin Bieber -- Treasure Trove of Drugs In Mansion During Raid

Justin Bieber had drugs and drug paraphernalia strewn all over his house when it was raided Tuesday ... but drugs were not on deputies' radar ... TMZ has learned.

Sources familiar with the situation tell TMZ ... when L.A. County Sheriff's deputies searched the house ... there were 2 large cookie jars filled with weed in plain view. There were also 4 - 5 empty codeine bottles in the mansion.

There were also 3 bongs -- 1 in the TV room and 2 in the kitchen.

There were styrofoam cups scattered throughout the house that had elaborate drawings on them ... including the names of the people who used them. The cups, we're told, were used for Sizzurp (also called lean) -- which is Justin's drug of choice. We're told he likes to draw on the cups with markers after using them.

And speaking of Sizzurp ... Sprite is usually part of the mix, but we're told Justin preferred pineapple Fanta instead. There were empty Fanta bottles that were discolored ... we're told from the codeine.

There were lots of "swisher sweets" cigars laying around the house -- Bieber's preferred way to smoke marijuana.

And speaking of weed … we're told Justin has a dedicated smoking room in the house, complete with hookah pipes. Sources say when cops showed up ... some of his friends went into the room and some of the illicit stuff went down the toilet.

As for why cops didn't seize any of these items ... law enforcement sources say they were not on the hunt for drugs -- they were primarily looking for video equipment that may have been attached to surveillance cameras. In fact, cops probably couldn't pry and open jars and such, because it would have exceeded the scope of the search warrant.

TMZ broke the story ... Justin has developed a serious drug problem and his people are pushing him to enter rehab ... something he has resisted.