My professional advice is to knock it over with a lawnmower, Then let the grass grow up around it for a few weeks until you forget it's there. Shortly thereafter, accidentally run over the pipe with the lawnmower in order to destroy at least one blade. When the lawnmower is finally fixed after several months, go mow the lawn again, which has grown to a ridiculous hight at this point. You can then forget the pipe ever existed, it's gone forever.
I've done this with several large metal objects, works well π