My experience was with the Panacur granules, but I noticed they have a liquid now. That might be more water soluble and better for soaking their food, but I don't know the dosages for it. I don't think it's real critical to be exact, however.
This was for my 20 gallon tank with Bolivian Rams, a pleco, a ghost shrimp and a guppy, so adjust as necessary -
Do a water change first, then thaw a cube of bloodworms (or anything they'll eat) in some water with 1/2 gram (half a packet) of Panacur and perhaps a little garlic to disguise the taste, then pour the entire contents into tank. Feed them nothing but same medicated food for 4 days, but don't add more meds to the water. After 4 days do a water change and vacuum. It usually takes two treatments to eradicate completely, so repeat the treatment after two weeks time.
You may lose some fish anyway, but not necessarily. One of my rams who was infested is still with me, as is the shrimp and pleco. Good luck, Tony!
Yeah it's really gross, and seems to be getting fairly common. Thing is, you can still quarantine and they might not show up until after. The fish usually show no signs of illness until suddenly you see those red worms coming out of their butts. My ram above was still eating and acting normally when I took that pic! Ultimately he didn't make it, but others did.