about dumping... press [ t ] and go over the trade depot to see the stuff in it. press [ d ] to dump an item and +- to scroll through (I think...)
or use the mass-dump shortcut that won't work

yeah, the setup looks kinda like this:
####V++
####.++
++D=~++
####.++
####.++
where # is wall, + is floor, D is door (optional), . is channeled out floor (NOTE: channel out AND REMOVE RAMPS TOO), V is down ramp (for access), =~ is bridge ( = is the thing that is anchored. press [ a ] when making the bridge to get it to raise left (west) )
have fun!