I was thinking 6" diameter schedule 40 and fitting a Duke 155 inside of it probably more work making the pipes and putting them to use than it'd be worth just an idea.i was going for something similar to minklessinpa but the white pipe planted in the bank of a ditch or something similar with maby an inch of water in the bottom of the pipe
I'm not sure if you have them in your area but around here we have culverts under the roads where a pool 4-12' wide will appear below it. These pools hold minnows and creek chubs, crawfish and frogs, (sometimes muskrats) all the thinks mink love to eat. At the end of these pools is a little creek/stream whatever you want to call it where the water is leaving that pool. If you can use a trowel or your boot and dig that deep enough to mostly submerge that tube you'll catch mink in them. A colony trap if legal works great there too, but they need to be completely submerged IMO so whatever you catch isn't fighting each other or the trap.