I will describe how to build a small motored water pump with a travel jar instead of the accepted bottle cap method. This will bring a number of benefits, including easy accessibility for repairs and adjustments of the internal fan. It's relatively cheap, functions well with vinyl tubing and, err... looks great.

Step 1: Materials

Materials need:

-Travel Jar of your choice of color (Bought @Walmart)
- 3v to 5v dc motor from disk drive, radio shack, hobby lobby, electric sharpener, toy, etc.
-make sure it has a gear
- glue gun
- 3 to 5 v dc output adapter such as a cell phone charger.
- plastic strips for building a fan rotor.
- Tubes for water inlet and outlet, i.e. from a pen.

Drilling/cutting tools for plastic:

- drill (or some other sharp metallic tube)
- micro torch or other heat source
- scissors

Step 2: Basic Component

Before you do anything, you might want to spray around the motor shaft with WD-40 to extend its life. Optional.

With a heated object (such as a metallic pen) and ample pressure, you will make perforations on the travel jar. You will need to make three of these in total. You can either heat the sharp object, heat directly onto the jar, or both.

-Inlet/Outlet Tubes:
You will need about an inch of tube for the outlet. About half an inch is ideal for the inlet tube. I cut a pen's tube with a heated knife. If you plan on connecting aquarium tubing to your pump, make sure it connects with the outlet tube.

-Rotor Perforation:
First make a thin perforation on the bottom side of the jar. It must be precisely in the middle. This is for the motor's shaft to go through. Make sure it fits in the small perforation before moving on.

-Inlet/Outlet Perforation:
Now make a perforation for the water inlet and outlet tubes so that when they are glued onto the perforation a 90 degree angle is formed. The top cap of the jar will be the water intake. For the outlet perforation, BE CAREFUL not to do it where the two parts of the jar meet. Also with these, make sure your tubes fit into them.

-Gluing:

Now glue the constituents onto their respective perforations, making sure they are water tight and sealed in place. Again, be careful not to glue the jar shut.

Step 3: The Rotor Fan

Make sure the gear fits snugly into the shaft sticking through its perforation. Then take it out and start working on the rotor blades.

Blades:
-You will need to cut out 4 congruent blades of plastic to glue onto each fourth angle of the gear.
-Make sure they're not too large that the jar won't close, and not too small as to lower its functionality.
-The depth each of my blades was about 1.3 cm. You can heat your scissor blades to make the cutting easier.
-Once you have your plastic blades, glue them onto the gears.

-Glue your fan onto the motor shaft carefully. You don't want the gear to be glued onto the travel jar...it won't rotate.

Step 4: Power and Testing

Now you must power the fan:
-Cut off what's on the power adapter's end and split the wires.
-Simply latch each wire onto the motor terminals.
-Plug in to test.

If you find the fan to be rather weak, try loosening the fan from the shaft a bit. If that doesn't work, use a slightly higher voltage. To test on water, the jar must be closed. Use a clamp or hands to hold the pump on surface of water being careful not to let the motor submerge.

Tips and Troubleshooting:
-Again, WD-40 will protect from water and deterioration, but completely optional.
-You can make it hands-free by placing it on a heavy base in the water or using hanger wire.
-If you hear the motor working, but the fan doesn't move, apply some hot glue in the gear and/or make the fan smaller
-If using aquarium tubing, apply the tubing after you let water run through the pump. If the tubing is on beforehand, it likely won't work.

Applications:
-use with aquarium tubing to transport water.
-distilling condensers
-irrigation
-small water fountain
-Terrarium river/waterfall
-many more