The mixing rate of a solution being added is dependent on flow rate, mixer speed, point of entry and solution concentration among a few of the variables.
A very concentrated solution can maintain its integrity for quite some time unless the stream is broken up by the mixer and even baffles which introduce turbulence to assist in breaking up bands or "tubes" of added solution. Imagine squeezing a tube of toothpaste into water. If you do it in a continuous stream you get a "tube" of paste in water. If you do it "somehow" in chunks, you get "drops" of toothpaste. It is the job of the designer to break up these pieces of whatever nature, in such a way as to achieve a good mix.
Now, our problem with Silver Nitrate is not as bad as using toothpaste but the analogy exists and if you add concentrated AgNO3 solution to water, you can actually see the "tubes" or "drops" and they vary with concentration, rate of addition and diameter or size of drop or tube.
You can experiment with this, as I did, with concentrated table salt or the like, with dye in it, added to plain water at varying rates, with different mixing and etc. This will "teach" you the optimum for any condition.
I get turkey basters at Home Depot, and I get large size (80 ml) from the Formulary. All of the tips have Luer connectors and I can exchange tips.
Expect some corrosion with cheap stainless. I try to stay with non-magnetic, non-plated parts, but this is not always possible. So, when things corrode I replace them. Oh, and standard tubing goes over a Luer male connector on a syringe and can be cut to any length and clipped in any position. I have shown pictures of that here on APUG.