Originally Posted by Jrex

This is how I did a waterspray for my 03 WRX sedan, it's cheap (around $150), easy to do and looks factory!

It involves putting a second motor in the existing washer bottle, the hatch has a second motor to power the rear washer so the space is already there, as is some of the wiring..

The parts you need,
From Subaru:
1 Motor SU-86611AC010 $36.40
1 Grommet SU-686223030 $3.35
1 Non Return Valve SU-786634050 $4.75
1 STI Nozzle SU-86636RA120 $32.40

2m Washer hose (Autobarn) $1/m
Electrical wire and connectors (Dick Smith)
1 Push Button Switch (Dick Smith) $2.00
1 Hobbs Switch (Robbos Campsie) $50.00
Total $140

You will also need a 20mm Hole saw and a test lamp!

First remove the washer bottle by disconnecting the wires and hose and undoing 2 phillips screws. Take it out and empty it.
You will now see the space for the second motor. Drill a 20mm hole through the raised disc section, the centre is marked for you. (Be carefull not to let the drill run off centre)
Clean up the hole and insert the grommet. Now just push the motor into the hole and check that it's water tight.

Now take a look at the loom and you will see an extra plug taped to it, this fits to the new motor and the wire runs to the right stalk at the steering wheel.

Connect the hose to the new motor and connect the old hose and all the wire plugs and then you can reinstall the bottle.
Follow the washer hose up to the bonnet and then route the new hose to the front centre of the scoope plate.

Drill an 11mm hole in the plate and then with a file notch a square section in the top and bottom of the hole so that the nozzle clips in nicely.
Now connect the hose to the non return valve and then the nozzle.

Now for the wiring, look at the wires at the new plug and take note of the colours, mine were yellow with blue stripe and blue with black stripe.
Take off the cover under the steering wheel (1 phillips screw then click it off) and then unclip the loom from the left stalk.

Locate the wire. Mine was the blue with black stripe. I located this by turning all power off and then connecting the blue with black stripe wire at the plug end to the + terminal of the battery, then with the test lamp I located the live wire at the steering wheel end.
To check that you have the right wire, connect the pump end back up, turn the ignition on and then connect the steering wheel end to earth (a bolt on the chassis). The spray should fire!
The worst you can do is blow the fuse!
I then connected two wires to this wire, one for the manual switch and the other for the Hobbs Switch.

1 of these I ran to the centre console and connected the button switch. (one side to the wire and the other side to earth, a bolt under the console)

The other one I ran through the firewall for the Hobbs Switch.

"T" the switch into a pressure line and then connect the wire to one side of the switch, the other side goes to earth.
The switch is pressure adjustable via a hex screw in the top, and you can test it with a bike pump.

Then your done!

Good luck
It might be a good idea to put a water only sticker on the bottle, so no-one put windscreen cleaner in it!