I used a bug spray bottle similar to Del's, did the trick for me. It allows a decent flow of hot soapy water to be directed down the drains to ensure they're clear. I haven't done the rears but I'm not too concerned. My cars stands facing down a slightly inclined drive so my assumption is that the dirt will always be exiting the sunroof area via the front drains, so they're most likely to block.
I removed the scuttle covers, saw there wasn't much debris at all, removed what was there, then flushed water through them and observed it exiting rapidly from both sides so I'm happy they're good for now
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Audi D3 S8 - 2007 - V10. B&O, Phantom Black, black and silver interior, and still completely standard with everything working as it should
Audi TT - 2015 - Ultra