Well, an in-tank filter sits entirely in the tank while a hang on back filter (HOB) hangs off the back of the tank with an intake tube that goes on the inside, and an outflow area that dumps the water back in. I asked because Whisper makes both kinds, but from your description it seems like you have the in-tank model. Here's what I did with mine when I first got it. You can tape the end of the tube to the back of the tank, but I found that mine stayed on just fine without being taped.
I also put some nylon over the bottom where the water is sucked in because I've found out the hard way over the years that it's better to be safe than sorry
. Oh, and make sure the edges of the plastic aren't pointy...I rounded mine off.