Please help me find this Kids Fantasy Film!?

All I can remember from this kids fantasy film is that it is rather late eighties or nineties. Its about this kid who gets bullied, and he is chased by the bullies into a sewer system. He jumps into this sewer, like a big hole underground and he goes into this fantasy world. Please don't get this confused with Neverending Story, similar scenario. The kid who gets bullied might even have a girl friend but i'm not too sure, please please help, i'm dying to find out what it's called! Thanks