You will need:
* A kitchen knife or utility knife
* Needlenose pliers
* Regular pliers
* A small Phillips head screwdriver
Step 1: Remove the Handle
A pair of wires runs up the inside of the handle to the switch. If you want to recover all the wiring in one piece, remove the screws from the handgrip (don't forget the angled one at the back) and pry up the lighter-colored pushbutton; the handgrip will come apart and you can slide the entire aluminum handle off over the 10A SPST switch inside. You can also just cut the wires.
Step 2: Remove the Rest of the Handle
Step 3: Disconnect the Mop Head
Unscrew the screw above the U-joint, then turn the pump assembly over and unscrew the screw in the center of the back (it was previously covered by the handle). Now go into the pump assembly from the top and unscrew the two screws that hold the pump to the housing.
Lift the back off, and pull the mop head free from the U-joint. Don't lose the screws, you'll need them later.
Two wires connect the pump to the battery pack, attached with a pair of battery clips. The clips slip right off, so if all you want is the pump and not the housing, you can remove the clips to take it out.
Step 4: Free the Nozzles From the Mop Head
Four screws are at the corners of the mop beneath the velcro, and the other four are around the part where the hose goes into the head.
Once the screws are out, the bottom of the mop head lifts off. The two nozzles are secured by molded-in plastic clips; the easiest way to get them out is to grip the dark purple plastic just outside the nozzle and bend it down, then slip the nozzle out.
Step 5: Two-way to One-way
Lift the T-joint and hold it firmly between your finger and thumb. Firmly grip the hose and fitting that attach the T-joint to the output of the pump (but not too firmly -- don't crush the plastic fitting or tear the hose) with the needlenose pliers, and twist back and forth to loosen. You can then slide the hose out through the mop head joint.
Next, disconnect one of the nozzles from its hose in the same way you disconnected the T-joint. Slide the fitting into the pump output hose, and now you have a one-way pump!
The pump runs on 6V (4 AA batteries). It will run as long as the circuit is closed (note that I haven't stress-tested it, so I don't know how quickly the motor will burn out). It might be possible to drive it from one of the 5V lines off an Arduino; if not, a simple step-up regulator should do the trick. I haven't measured the flow rate yet, but I plan to do so at full power and at various PWM duty cycles; watch this space for details!