Spare cassette waste tank suit the Left hand C400 series of thetford toilet. If unsure if its left or right, check location of the small green valve knob.
We have been selling this product for several years now. These are popular with our customers and we sell a number per week. We try to keep a few of these on our shelves for quick delivery. If you order more than the 11 we have in stock, the delay is around 9 days to get more.