It seems the push-button of my Porta Potti is broken and I found only white button and metalic spring. I lost all what could be under cover. Can I by it anywhere? Where?How can I repair it?

SOURCE: Cleaning a thetford porta potti

You can get the manual here.
http://www.thetford.com/Home/Products/PortableToilets/PortaPotti135Marine/tabid/96/Default.aspx

Good Luck and Please Rate FixYa!

SOURCE: metal spring has broken under my gas pedal

Put the Brake spring under the gas pedal (think its the same part) and then get a "Squash Ball" (small hollow ball for the game Squash) and tape that in place of the spring, you brake pedal will now feel more firm like a real car....

SOURCE: Instruction Manual for Porta Potti

Hey,
Here is the link. You can find the pdf on the right hand side of the webpage. 
http://safemanuals.com/user-guide-instructions-owner-manual/THETFORD/PORTA%20POTTI-_E

Hope this helps
Thanks

SOURCE: Need instructions on how to empty Porta Potti 165

Your lucky day I found the answer to your problem. I also need some info and checked out the net.
Just go to www.thetford.com
You should be able to find a download for your potty as I did for mine!
Hope this helps!

SOURCE: Flushing knob on a C2 Theford cassette porta potti hard to turn

Hi! Spray blade which closes holding tank with silicone spray. Make sure spray goes under lip of sealing ring. Also spray around holding tank actuator knob allowing to penetrate underneath to shaft. Don't use a silicone grease as this will gum up the works. If you can't get hold of a light silicone spray try using household type silicone polish intended for furniture. Wipe off any surplus as only thin film required.

John Long