Pump sump/reservoir for Hot end coolant.

thingiverse

Uses aquarium pump: http://www.dx.com/p/334988 to push the water. My first print leaked slightly, the wall thickness of the reservoir is 2mm. Try setting a wider nozzle size than you are actually using and run the printer a bit slower to ensure you can push the extra volume of filament, This will build much better inter-layer bonding. Set 100% fill also. If using a tall rostock, mount within 500mm or less of the top of the water tubes to help priming. You will probably need to prime the pump as the way I have it oriented, it will seal against self priming. Put someprotective plastic sheet down and towel and siphon to start then seal up.