ashcatcher on my bong?

Hey i just bought this bong and i was wondering is i could get a ash catcher cause i dont want it getting dirty in it. And what i would need to buy for the ashcatcher. Is there a certain downstem i need for it? I recently bought a 9mm downstem for it. Thanks! And

The water is there to catch the ash, just rinse it... The ash isn't what stains the inside tho, it is the smoke... When it gets scummy, just rinse it in 90% rubbing alcohol, let it sit in the bong for a few hours, swishing every so often, then you will have a clean bong... it is called maintenance..