i do the same thing with cuttings closest to the top & the bubble cloner.
Yes people do it that way too. Some people PM'd me for more info. This is what I said. But the bubble method is a really good choice.
There are a couple posts/threads on ICmag about rooting cuttings in water and in those threads or a separate one was people who sexed cuttings in water.
I have done it many times now. Sometimes strains sex fairly quickly in 5-7 weeks from seed popping out of the ground. But many times I run into seedlings that have not shown sex in 9-10 weeks or more. So I started doing it with cuttings.
I let the seedling get big enough to take a cutting. You can let it grow for 4 weeks so it has say 5 or 6 internodes. Then top it so you have a cut with 2 or 3 leaf sets on it. Or use a side shoot if you have any.
Then I use white bathroom cups or whatever plastic cups you can mark and mark the mom and the cut A or 1 and the next one B or 2 so you know what cut came from what seedling.
Now mix up some 1/4 strength fertilized water and put enough water in each cup you have a cut in. Stick them under 12/12 and they will start to flower. They will probably also root but will need revegged if you use them.
You can also just soak peat pucks in the fertilized water, let them swell and stick the cut in them and put in the cup. Don't squeeze them as dry as you do when you are cloning but squeeze some water out of them. Keep them moist until they flower.
They will start to show flowers in 10-12 days.
I have a container and a piece of styrofoam that can float in it without hitting the sides. I poke holes for the cutting stems to fit through. The holes are labeled 1 through 10. Then on a piece of paper I mark 1 to 10 and what strain each one is. I can use the same piece of styrofoam over and over.
Those little styrofoam plates that hamburger and stuff comes in... the pink ones make a good float.
When you use the float method the cuttings are always in the water even as the water level drops.
If you don't put something in like SM-90 to prevent rot or stink water just change the solution every couple days.