This article is about a plastic bottle submarine that sinks but does not rise:

You can see that I used cheap blue tack for water insulation.

The water pump is driven by a 12 V battery.

Watch the video of the submarine:

Step 1: Make the Rectifier

Most cheap water pumps cannot pump in reverse. If you switch the electrical polarity then you will damage the water pump. This is why you need to make a diode rectifier. I made the rectifier with a Schottky diode that has a low forward bias voltage.

However, you do not need a Schottky diode because most water pumps need between 5 V and 12 V input, making the 0.7 V voltage drop almost irrelevant. Thus you can use a normal diode. You can order a 5 V pump with a USB plug thus eliminating the need of building the rectifier. Do not exceed the maximum input voltage of the water pump.

Step 2: Attach the Pump and Drill the Hole

Your hose must fit the hole of the water pump. Thus you will need to order hoses (to see which one fits) of a few sizes and this can cost money. If you are using more than one bottle then you will need a fitting.

I made a hole with a hole puncher.

You can also use a soldering iron.

Step 3: Testing

You can see that the water exits the bottle through the hole at high pressure:

Conclusion

If you want more challenges then you can make a submarine with more plastic bottles. 

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