but isn't it a drag

reaches forward and touches the pipe w rh (to be fair, given the way he's standing here, his rh is his downstage hand, so this could be more about blocking here)

holds envelope with lh and pulls the tape out with rh

tries to use the key with his rh

reaches into envelope and pulls out the tape again w rh

sets the tape down and supports his weight with his lh as he gets on the floor

reaches for the tape player w rh

tries to throw his shirt for the tape w rh

holds shirt in lh while he feels around/gestures w rh

reaches in the tub for the plunger w rh

ties plunger onto his shirt with and uses his rh to try to get the tape recorder

holds tape recorder w lh, puts tape in w rh

holds tape recorder w rh as he listens to it (which in this instance might be more of a blocking thing like with the pipe more than a dominant hand thing, though at 11:07 when he plays Lawrence's tape, he still holds it up with his rh which is not his downstage hand in this position)

I think the point has been made here, but let's skip ahead to a couple other memorable parts in the movie:

Adam reaches into the toilet bowl and digs around w his rh

reaches into the toilet tank and lifts out the bag with his (non poop covered) lh

he pulls the saws out of the bag with his non poopy lh but uses, breaks, and throws the hacksaw with his rh

Adam is resting his weight on his rh when it cuts back to the bathroom after Amanda's trap and gestures w his lh, but i think this is more about the blocking and camera position here

he reaches forward to pick up the mirror shard and threaten Lawrence with his rh which is not his downstage hand here

picks up and throws stuff at the mirror with his rh

picks up Lawrence's wallet with his lh, which is the one closer to it (the one he uses to hold it and dig for the picture of Alison and Dina switches between shots)

Adam does smoke with his lh in the bathroom, but he picks up and uses the lighter with his rh, and as a right handed stoner, I most definitely light my shit with my right hand and hold a joint/pipe/bong with my left (he also reaches/gestures for the cigarette with his rh when he's asking Lawrence to give him one, which is his downstage hand)

Adam is smoking with his rh when he's walking up the stairs to his apartment, shuts the front door with his rh, is carrying and throws his keys on the table with his rh, has the camera hanging around his shoulders so that the camera is hanging on his right hip next to his rh

beats up Billy in his apartment w a baseball bat w his rh

approaches his closet door with the camera in his rh and the bat in his left, also opens the door with his left

holds the camera up to his right eye to take pictures of Lawrence ("BUT THAT'S HIS EYE" you say- well typically people are right or left eye dominate in the same way that they are right or left hand dominant and usually that dominance is on the same side, so unless he's a right handed left eye dominant freak like me, he is likely right eye dominant and therefore also likely to be right handed)

that said, he does appear to be holding the camera to his left eye when he watches Lawrence go into the motel room

he does throw the stack of photos at Lawrence with his lh

he takes the money from Tapp w his lh

picks up and throws things at Lawrence with his rh after he gets electrocuted when he's begging him to get up

he punches Zep in the face w his lh while pinning him down w his right arm, after getting shot in the right shoulder

not surprisingly, he uses his lh for most things (reaching for Lawrence, searching Zep's body for a key, holding and listening to the tape recorder) after he gets shot in his right shoulder

he does dive for, grab, and take aim and John with Zep's gun with his rh (and Adam died for it)

So while Adam does use his left hand for plenty of things that don't always seem related to blocking, given that he uses his right for more fine movements like loading the tape recorder, using the lighter, and it's his throwing arm, I'm inclined to say that his right hand is dominant