Hi Danny
The flushing reservoir is built into the toilet.
When you open the door on the outside, you should see....
Top.... a filler neck that swings out with a yellow lid on it and a small yellow cap below that. This is the toilet flushing water filler neck. Pink stuff and water goes in here. Some Pink stuff and a lot of water.
When full this is the water you will see if you remove the toilet roll holder, where the pump is hidden
To the right and just behind the hinges, you will see a small vertical clear pipe connected at the top to a rubber bung. This is the flushing water level indicator. The water level will rise as you pour water into the filler neck above.
This pipe can be unclipped and pushed down to empty flush tank before a journey to save towing a few gallons of water about.
The second part of the system is the waste part...the bit you empty. This is where the Blue stuff goes.... again just a bit as per instructions
Below the filler neck you should see a grey box type of thing. There should also be a yellow clip.... about 4" x 2" which is spring loaded...push down and pull out grey box. Toilet flap inside van must be closed to allow the box to be removed.
The grey box is the waste tank. When you get it out it should look like this
http://cgi.ebay.co.uk/THETFORD-C2-3-4-CARAVAN-TOILET-GREY-WASTE-CASSETTE-TANK-/360255764397?cmd=ViewItem&pt=UK_Campervan_Caravan_Accessories&hash=item53e0eab7ad
Slide the grey box out and empty at Chemical Disposal point on site. Just twist the curved neck 90 degrees, remove cap and pour out to empty. There is a yellow button at the other end of the waste tank.... press this while you pour out waste contents...it is an air valve and will allow "smoother" emptying of contents.
Refit is the reverse...