It is called Fertilizer Injecter System EZ Flow makes one, it is the one I use. Comes in 3/4 gallon, or 3 gallon. Attaches right to the faucet and drip system. It has male and female hose connections.

Here is a link that might be useful: EZ-Flo

Although I thing fertigation is a bad idea under any circumstance except commercial growing operations, they are available. The one thing that MUST be addressed is PROPER backflow prevention. Under a typical residential setting, an RPZ backflow preventer must be utilized to prevent the contamination of the potable water supply. Unless of course you care to run the risk of poisoning you and your neighbors drinking water supply.
However, the thought of SOME of the neighborhood children playing in pesticide treated irrigation water does seem somewhat amusing. You know how kids just love to play in the sprinklers!

All Wet
Texas Licensed Irrigator #1897 since 1984

Thanks for your replies!