I've been using dosing pumps for a while. I use the AquaMedic Reefdoser pumps.

I have the lines plumbed into the returns of my cannisters using a type of T in the cannister hose with a 4/6mm inlet (Meerwasser Shop aquaPro2000).

Pumps have varying flow rates depending on the make and model. Some have flow rates that can be set, others have a fixed flow rate of x ml per minute. The dosing is simple. Just mix up a batch of macros and micros that will give you whatever mg/l dose you want into the tank. For example, if you're currently dosing 30mg/l of NO3 into your tank a week, just mix up a batch of KNO3 that will dose about 4.3mg/l a day. Or you can break it down further and dose several times a day if you want.