My tub and alley is open bars that cattle can see through. I try to limit to 3 cattle in the tub, which is what also fits in the 30' alley. To fill the alley, the person working the alley steps to the "dead corner" of the tub and the first animal naturally steps into the alley, push that one up and the other two follow in. The tub gate can then close off the alley or put a stick in and go get 3 more for the tub. If I'm by myself, I can usually fill the alley from the tub and leave the tub gate closed to hold the alley and work the ones in the alley through the chute. The portable tubs I borrowed were full sheeted sides and the cows just balled up in the tub and wouldn't go down the alley.
I had a bud box in a couple different set ups. Non-gentle (not wild, but not pets either) worked fine in it. Old show heifers just wouldn't go up the alley from the bud box. We still have a few and they work fine in the tub. I took a couple pics of the tub and alley I built in 2021-22. Planning to put the chute on concrete with a scale set up before the chute and will probably tune on the alley some more, but this is functional now and I AI'd 60 cows through it last spring working mostly by myself.
First pic is from the working side of the chute and alley. Second pic is from the outside (non-working side) showing the load out that comes off the tub - the gate to the load out shuts off the alley if using the load out. Third pic is the load out gate from the tub. Next project is making the load out permanent, then raising the overhead bars on the alley and building a scale section with a slide gate on the back right before the chute. Notice my high class working table chute side :cool: