You might be searching for a pump that operates on 3-6 V and gives an output of above 70 L/H  then this could be the best choice for your project.

This DC 3-6 V Mini Micro Submersible Water Pump is a low-cost, small-size Submersible Pump Motor that can be operated from a 2.5 ~ 6V power supply. It can take up to 120 liters per hour with a very low current consumption of 220mA. Just connect the tube pipe to the motor outlet, submerge it in water, and power it.

Note:

1. Make sure that the water level is always higher than the motor. The dry run may damage the motor due to heating and it will also produce noise.
2. This product is available in two different colors like Black and White, which will be shipped randomly so please note you will get anyone out of both colors.

Features: 

• DC 3v to 6v submersible pump
• Micro Mini Submersible Water Pump 3v to 6v
• DC water pump for DIY
• DC pump for HOBBY kit

Package Includes:

1 x DC 3-6 V Mini Micro Submersible Water Pump