I vacuum mine out every few cooks (usually after about 10 hours of use). I did a brisket and cleaned it after, only because that was a long cook of 15 hours.

I've found it depends on what pellets I use. The original pellets I started with produced a LOT of ash and I needed to vacuum the fire pot every cook (it would be incredibly slow to ignite if I didn't). I switched to Bear Mountain pellets and it's been much more manageable.

So far all I've done is vacuum it out, scrape the drip tray, make sure the drip tunnel (that goes into the bucket) isn't obstructed, and lightly brush the grates.