I'm a chemist, so I am familiar with some of these things in other applications.
I personally would not use bleach in any dilution. The ingredients that make bleach what it is are not volatile. I little rubbing alcohol left in a syringe will at worst make the juice funky and pack a serious cough hit. A little bleach (hypochlorite and hydroxde) accidently left in a syringe, and then into a juice, will destroy tissue. 8-o
Nothing grows in PG that you are going to have hanging around your home, and few things grow in VG. Vodka will kill most things, rubbing alcohol will kill most things (good enough for a doc to put a needle in you!).
I keep a jar of about 100 mL of vodka with my mixing stuff. After I use my syringe for making a juice, I dip the needle into the vodka, draw the entire volume of the barrel of vodka into it, squirt it back into the jar. Do it again, and the syringe is clean and sterile enough. Use the plunger to repeatedly and rapidly push out residual vodka until nothing sprays out the needle. Done.
When carts are used for a few days, they are done. I remove the filler and straw, toss the cart housing into vodka, combine the fillers into a syringe and press out the juice (generally delicious) with the plunger, then put the filler material into vodka along with the straws. Next morning it all comes out and I lay all cart contents (save the juice) on a paper towel to dry for a day or so. All clean, all flavor removed, all sterile as is needed. The fillers comes out like new.
Same thing with empty juice dropper bottles. Get the last liquid out and toss them into vodka. remove them after a bit and let dry. done.
Since vodka kills most things, all I have to worry about with it is residual flavors from all the above. And that takes about a week before I decide to put in fresh vodka.
The only thing I have that is long term stored is high-nic unflavored juice. Flavors can decompose on their own with time, depending on amount of water...which can increase dramatically if the liquid is very cold and exposed to air. Flavors for me are short-term only, and small amounts. Sun has an interesting story of how his still-sealed flavored juices went bad in his fridge after only 6 months. If you know the chemistry it makes perfect sense. See the threads on juices going bad. Sorry, but I have discussed and answered so many repeating questions on the subject that I think just searching and reading will take care of your questions.
I also had the marking come off of my syringe. Not sure why they sell DIY vaping mixing syringes with marking that are soluble in PG or VG, but there it is. Before that happens now with a new syringe, I use a knife and carve graduations into the plastic for mL and 0.5 mL. You can ballpark the in betweens. I thought about the pipet thing, and it may be a great improvement, but I've not used them for DIY, and I tend to spill more with pipet/bulb combos. Syringes are perfect for me.
All vodka procedures can also use rubbing alcohol instead. Just make sure the items are completely dry of it, like dry them for at least 24 hours. I avoid the stuff for now because I don't want to taste any accidentally. residual vodka just makes the juice more hitty and gassy, as in gas expansion. Depending on the denaturant used, there may be a horrid tasting residue of pyridine, or a a denaturant that evaporates along with the alcohol. Not sure they have to say what it is. So I avoid it, also for the reasons above.
Since I only make up 4 - 6 mL of a flavored juice at a time, use it, then clean everything and start again, I am dealing with cleaning a relatively limited number of items, which are continually being recycled back into the mix. When mixing, clean needle goes into unflavored high-nic juice first, then VG, then flavoring, then juice bottle, then vodka, in that order.
Other tricks too I can think of. This is plenty for now.
Have fun!