I use an air pressure system to add my evap water. I imagine you could do something simmilar to dose the part one and part two. You would need 1 small air pump, a two port air distro ( can be found at wal mart) Some airline tubing and a drill. ou will also need some silicone to seal the holes in the cap. Drill a whole in the bottle caps. Run airline tubing from the air pump to the distro, then to each of the bottles. Then run another air tube from each of the bottles to your tank, this line should go all the way to the bottom of the bottle. This will be the dosing line. Seal the left over space in the bottle caps. Now when you start the Air pump air will fill the bottles and will force the fluid to flow to the tank. You can adjust the flow by setting the Airline distro, or by tieing a knot in the airline goinng to the tank.
I hope this helps.