This is, like Julian's Thing, an applicator, but is easier to use and more versatile. It is very simply just two similar lengths of poly tubing of different diameter slid inside each other. It is used with the syringe of your choice. The 3/8 outer tubing I use fits perfectly snugly over the end of an insulin syringe. With it I can load the syringe with colloidal food suspensions or aiptasia-x (with a larger bore needle), or acid for injecting unwanted polyps, etc (with a smaller bore needle). The syringe is fitted into the larger tube and the smaller tube slid down inside and pressed to depress the plunger on the syringe and dispense the contents.
I know it's kind of stupid simple but I can manipulate and aim the needle really precisely with it and control the amount I dispense really well too, without getting my hands in the tank. My Thing is slightly curved (it's true) to allow me to get around and under things a little better. The curvature could be increased by heating the outer tube and bending it if needed and it would still work well I think. It could also be adapted for larger syringes I'm sure by using appropriately sized tubing.
I know it's kind of stupid simple but I can manipulate and aim the needle really precisely with it and control the amount I dispense really well too, without getting my hands in the tank. My Thing is slightly curved (it's true) to allow me to get around and under things a little better. The curvature could be increased by heating the outer tube and bending it if needed and it would still work well I think. It could also be adapted for larger syringes I'm sure by using appropriately sized tubing.