Where can I get a replacement clip for the lid of my Vax 2000

This appears to be a Vacuum rather than something for the Cars and Trucks category. Moved to Vacuums.

This is a very obscure make that is only available in the UK. I remember them for carpet steam cleaners years ago. We are in North America. Try contacting their support direct.

https://support.vax.co.uk/

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https://www.youtube.com/watch?v=uLIlPuc4MbE

Rinse the dirty water tank and lid under water (max 40oC) to remove dirt/debris. Clean the filter screen located at the back of the dirty water tank. To re-fit, tilt the dirty water tank and line the front of the tank up onto the carpet washer. Push back until it clicks into place.
http://blog.vax.co.uk/cleaning-maintaining-vax-platinum-power-max-carpet-cleaner/

Sometimes there is a tiny speck of dust caught between the top of the canister and the lid. Unlock lid, with a slightly damp tissue wipe around top on canister and then the rubber seal in the lid, dry with dry tissue, put back together, noise should be gone.

Below can be found the downloadable user's manual for the Vax 2000 UR vacuum. If that's not it, check the manuals on the second link.

http://www.vax.co.uk/downloads/pdf/u90-vu-series_user_guide.pdf

http://www.vax.co.uk/support/resource_centre.php

I have just downloaded a manual for the VAX 5130 from here:

http://www.manualnguide.com/dl/20364/

Remove the two screws from the top cover, remove top to expose belt & replace. Replace top cover.

Set up is complicated unless you are patient.
Remove the paper dust bag from the bottom of the canister and then filter ring. Then put in the recovery bucket of which 4 litres of warm water should be added and a capful of floor cleaning solution.
Then remove the pump wire on top of the Vax motor where the blue filter circle is (keep the filter in, do not remove it!).
If the 2000 has a separate pump notch on the rim of the Vax motor head on the outside then you should plug the black cord in that has a washer screw type metal connector. Push, twist and lock in. Then the black cord which eventually leads to a clear pipe with the older clip on wash handle that has to be clipped to the main hose handle has to have the black and see through cord clipped to the main hose and eventually down the extension pipes until you get to the floor head. If you have the older style T shaped floor head the cord should slip into the floor head easily. Then either squeezing the trigger to release the cleaning solution in, switch the Vax on and hit the secondary pump button. This will pump the cleaning solution and water into the carpet. To stop the pump you can either lock the wash trigger to stop the liquid or squeeze the trigger to make sure no other liquid comes out. Generally you can see the foamy carpet solution flowing through the see through rubber hose and eventuallly through the floor head.
To **** up the rest of the carpet solution, stop the pump button and the Vax can be used to **** out all the dirty solution/water in the carpet. Its a big and tedious task generally!
See an alternative manual for the Vax 1000 which is an older model but similar to the 2000. It is free and in pdf downloadable form:
http://www.vax.co.uk/downloads/pdf/VaxGuideNo8a.pdf

If you want a manual for the Vax 2000 hopefully the one on the Australian website will help.

Try http://www.vax.com.au/Downloadsusermanual.html and you'll see V2000 listed.

The 121 should only have the main filter ring taken out before the reservoir tank is put in which easily just falls into the main dust tank area. Make sure though that the bin's square edge is at the front where it rests at the front of the Vax where the hose comes out. Then unhook the pump to lay it in the water tank and the motor should be able to jam ontop clipping both sides down to lock. Perhaps you are putting the reservoir bucket in the wrong way.