It sounds like you're doing enough cleaning. I prefer to call it 'residue'. It's not the smoked gunk that collects in bowls. It's condensed vapor, and it can be reused. I've used vapes that were in desperate need of residue cleaning and never had a "bad smell/taste" other than the overcooked taste of 'finished off' herb. Are your leftovers really dark? Getting the smell/taste at the end of the bowl maybe?