Charles Harrison (owner of the referenced website) happens to hold a Ph.D.
I've purchased from Doc several times without complaint.
Flubendazole and Levaisole hcl are water column dosed.
+1, I ordered the levasole(levamisole) from Charles too, one package less than the recommended dose, the worm disappear over night, have never seen them again in my tank.
before I ordered the levasole, I used pure fenbendazole 50-100 times more than the recommend dose for two weeks, both in fish food and water column, only suppressed the worm (or possibly wipe out the eggs) , but didn't kill the adult worm.