It needs to be level, and also you need to use some type of funnel/hose...it may only LOOK like its overflowing, take a rag and put it around the hose to block off the 'leaks' around the hose or funnel your using and make it all go in...

I know when i did mine it took over 3 quarts due to all the stuff i spilled, even when like Daniel said, it only takes 2.3