Through all of my research, there are two main methods for injection in residential systems that are options for me.

The first (used by EZ-FLO jugs) is to use 2 hoses from a line (either to all valves (before) or to a single valve (after)). This method seems to always fill the tank with incoming water line 1 and pushes the water out (as well as natural suction out) of the second.

The second method is to use something like a Mazzei/venturi system that only uses one hose as suction out of the tank. Either you can buy an expensive Mazzei type connector (expensive) or you can make one for pretty cheap with some 1/4" hose and pvc.

The Mazzei/venturi system is installed on a bypass system to control the output mix (as well as a valve on the suction line itself) and the 2 hose method has a valve only on the outgoing hose to change the output levels.

First question is, which system is better for a typical dummy user to control output? The first seems to dilute the contents before injection, and the second seems to take the mix and inject it directly. Are there any benefits to either way?

Second question is, how to figure out what kind of mix ratio is going out on any given valve setting.

Third question is, with the two hose system, is it necessary for the water-in line to be near the injection point/line or can it be off of a separate water line?

I have yet to have someone explain the advantages of this fertilizer system that makes sense. There have been many past threads on this subject. The traditional method(that is why it is the traditional method)is easier, more efficient, more dosage controllable, does not affect the irrigation system itself over time and doesn't cost any initial cost or equipment installation. Why go through the hi-tech agony your questions illustrate? Sorry to be such a negative vibber, must be something I ate. JMHO GL Aloha