I was given an XP4 that had only been used once as a demonstration, but it had no pipework with it. Ever since I've had it it has been very noisy, kind of a buzzing/rattling sound - like it has air in it. What's the best way to prime it without the standard pipes, and get all the air out? I think that must be the problem, as occasionally if you shake it, bubbles come out. But I can never get it all out. At the moment I am priming it by starting the syphon by sucking the hose.