There are 2 ways I rig for fishing eggs under a float. Fixed or sliding. Fixed works best in water under 8' deep and swifter moving water. For a float I use the Canadian style dink float. For wieght I use enough o load the float so only about 1 and 1/2 inches is above the surface. I either use hollow 1/4" inch pencil lead that Islide up the mainline below the float or a slinky. To use the lead slide it up the line then slide a small bead on the line thn tie on a barrel swivel. Tie your leader on the other side of the barrel, add bait and your ready to go. I like to set the depth so the lead is just above the bottom. To use a slinky for wieght. Put your float on the mainline. Tie on a #7 snap swivel, attach a slinky that is heavy enough to load the float to the snap. To the other end of the slinky attach another snap swivel then your leader. Fish this the same way as you would with lead.
Now for the slidng float. I use a cigar shaped float like a Thill. My favorite is a West Coast Float that is made to be used with 1 ounce of wieght. To rig this way, Slide a 5 to 7mm bead up your mainline. Then slide on the float. to the end of the mainline tie on a kidney shaped trolling sinker. 1 ounce to an ounce and 1/2 are what you should need. The amount of wieght is determined by the float. You need enough to load the float so about and inch to an inch and 1/2 is above the waters surface. Use the sinkers that have swivels on both ends. Tie your leader to the other end. Leader length should be around 24 inches.
Okay, Now you need a bobber stop. If you dont now how o tie one just buy the pretied ones. Just put it on befor you put on the bead and float.
The slip float works best in slow deeper pools. Depth depends on where fish are holding. Ive fished the bait anywhere from 5 feet to just above the bottom in 28 feet of water.
If you are targeting steelhead use smaller hooks, size 2 to 1/0 and smaller baits. If you are after chinook use 3/0 to 4/0 hooks and bigger baits. Always use yarn in the egg loop to keep the line from cutting through the bait. Plus it acts as an atractor and scent holder.
Always use a flaotant on your mainline to help keep it on the waters surface. Musclin(sp) works best.
Good luck