Is your toilet a low level type with the "L" shaped pipe between pan and cistern? If so, check the pipe is not pushed in too far to the back of the toilet as it can be partially blocked restricting flow.
Have you connected it to the drain using a flexible pan connector? If the fall is not great, the corrugations can cause the flow of waste to be interrupted.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!