This instructable will show you how to turn a aquarium (blowing) pump into a vacuum pump.
The pump is a EHEIM 200 and costs about 10 dollars.
It's fairly easy to do and many other pumps work the same so you can apply this instructable to them as well.

Step 1: Open the Pump

Start by turning the pump upside down and open it up by removing the four corner screws.
Also remove the four silicon protection parts and lift the bottom shell.

Step 2: Remove Core

Remove the core of the upper shell by removing the six screws shown in the picture

Step 3: Remove the Diapraghms

Remove the diapraghms on both sides by removing the two screws on both sides.

Step 4: Remove the Valves

Remove the valves by removing the the bolt. On the other side there's a nut. They're attached together.

Step 5: Remove Small Pin

Where the valve was attached, there is a small pin that prevents you from placing the valve in wrong direction. We actually want this to happen because then the pump will suck. So we need te remove this small pin.
A good way to do this is with a Dremel.

Do the same on the other side

Step 6: Reverse the Valves

You can see also a small pin on the bottom of the valve. This pin was also placed there on purpose. Because normally you would not be able to place this pin in that way that it's on the same side as the earlier removed pin from the white part.
But now you've removed the white pin, you can place the valve with the pins on the same side.
Do this also on the other side. The valves are now turned and will make the pump suck.

Reattach the valves with the bolt and nut.

Step 7: Assembly Back Together

Place everything back together:
- First the diapraghms, then the four screws
- Next the core in the shell, then the six screws
- Close the shell, then four corners screws
- Silicon protection parts.