Yep, a network of tunnels was built under the Portland city center back when it was still a town, and yep, the occasional drunk was towed through them to the waterfront and stuffed onto a ship, where he got to "volunteer" labor in exchange for transportation. But that's not why the tunnels were built:
“Crimping or shanghaiing was quasi-legal in Portland,” Moore explained. “So there wasn’t any reason for you to do it under all of this skullduggery.”
No, the tunnels were actually built following the great Mann-made global warming flood of 1894 to drain water out of the basements of buildings in the area and facilitate transfer of goods to and from ships at the Willamette River waterfront. And while they were most certainly used on occasion to move unwilling men into forced labor on ships, that wasn't the reason behind construction of the tunnels, which eventually became notorious for opium den activity under the Chinatown area as well as other issues.
Most have been blocked off over the years.