You may be right in needing an injector that creates a positive pressure to work properly. I thought my problems were solved with a Dosmatic injector but if the back pressure, created by slow drip rate, is created it will not siphon fertilizer solution into the line. My best success is to put my fertilizer into a sprayer tank and pump it up to pressure with the line feeding into a simple brass siphon fitting. It is crude and less accurate but it seems to work.

Get yourself 2 or 3 55 gal drums and a small drop in sump pump While you are drawing out of one your filling the others . Have a jug of mixed fertilizer and away you go. I use this system in the late winter when the plants are small and the need to feed isn't great. Works For Me

I used a hozon for a couple of years, and then switched to a Chemilyzer injector. It's wonderful, and I would buy another one, I've had no problems. I mounted mine to a handcart to make it portable, and use a 5 gallon bucket to mix my fertilizer solution in.