I'll try and walk you through installing one version of IC spray system. First I need to acknowledge my friend Steve (300Z TT!) who w/o his electrical knowledge I'd still be staring at the pretty parts.
First parts need for this particular install. I used a dual pump washer bottle (one pump to run the windshield wiper fluid) the other for the IC sprayer. These are oem on the WRX wagon as well as other Subaru models- you may be able to find one used. Next you need some washer hose- sold in 6' lengths at almost all car parts stores. You will also need nozzles- I used the oem STi nozzle (mine only utilizes one as it is a RA splitter). You need a switch- I used a STi oem switch- the manual one. You also need some wire and four female spade ends to fit the spade ends on the switch. They are small and may be difficult to find- I found mine at a Chevy dealership looking through boxes of connectors.
First you need to remove the old washer bottle, two 10mm bolt heads, the plugh in to the washer pump and remove the hose leading ut of the unit- fluid will come out after you remove the hose.
You can mount the new one in, reconnect the washer line and add your own hose to the second pump. You'll see there is a second plug in already there for the second pump. Note the colors of the wires- yellow/black and green/red on the washer pump plug and blue/black and white/orange on the 2nd plug.