So I've got a few spots where I'll be trapping that I've seen otter sign on in previous winters. One spot is the outlet of a lake that stays open all winter. Unfortunately, because of the Greens, it's within an area where traps must be submerged, under ice, enclosed, or three feet above ground. I was thinking of setting some buckets underwater. My question is do you just set the conibear in the bucket? Do you try to set the bucket at an angle or just upright facing the surface? Do you place bait in the bucket or is the bucket an attractant/curiosity alone? Are there any other sets that would work in a situation like that?

I believe the bucket set has a fish tied to a rock that is fastened inside the bucket. railroad tie plate would likely work better than a rock.
I believe the bucket sets upright on the bottom.
Seen the set in print but never used it.
Lots of beaver dams here so never really bothered to try the bucket set.
I would probably give it a shot if I didnt have other options.

I've not played with it, but I've been told that a piece of culvert sunk in the crick with a trap at both ends and a visual bait in the middle is more effective.

Might be worth a try.

I've heard others talk about it. The usually use them on dock legs at the bottom. Heard they work real well.

I use a lot of bucket sets, but never used one submerged. Mine are normally set in 1-3" of water with the opening facing the bank, foot or two away from the bank. For bait I use mink or bobcat gland smeared on the back wall of the bucket, and maybe a wing hanging in it, a couple of feathers on the bank. It hammers them. But, I have never heard of anyone down here using them submerged.

I use a milk crate set open end up completely submerged. Weigh it down with a brick or rock along with a fish. I put mine in the middle of the river under an old bridge. Checking it is easy as look down from the bridge.

20 can you post a pic?

Sorry but I don't have one. It's just an upright milk crate with a 330 set on the top.

Dang, I did the same thing for mink many years ago with zero results. I used them boughten minnow traps, split them in half , closed off the big end left the cone on and used live minnows. I made a little extension of tin with a slot for a 110. My sample size was four but never caught anything. Otter were very scarce then. I really like your milk crate idea and like I was going for, completely freeze proof and no worries of water fluctuations.

Years ago I hear blue was the go to color.

Shhhh!! Don't give away all my secrets...

I'd go up and down steam. Then set where the otters tell me they want kilt.

X2

Do you put a foothold in front of it or use a 330 ?

I sink a bucket with some crab shells in the bottom in the harbor sometimes. I just put a rope through the spring of the 330 and tie it off to the bucket handle and put a buoy on it. Works for sea otters too (don’t recommend setting in salt water unless you’re a tribal member)

I use a 220 in the bucket.

I know this isn't what you asked about and not a bucket set but the otters I have trapped in feeder / outflow creeks have all been in double door cages submerged with a dead fish wired near the trigger submerged in a narrowed section of the creek. Have even narrowed creek down with wood fencing. Have the fish wired through the gills or eyes to the bottom yet able to "float" as if swimming in the creek. The creek flow moves the bait fish usually perch..