Yesterday, I cleaned out my W2 435 for the first time since install GGs. What a difference!
I always scrape out the firebox after every 5-6 uses, to prevent grease fires. With regular grates, I don't have to tell you what kind of sludge accumulates both in the box and in the disposable foil pan.
With the GGs, I found very little sludge. Most everything was carbon. Plus my flavorizer bars hardly had to be scraped of anything. I used a paint spatula to scrape everything down into the foil pan for disposal. It was so dry that I could tip the foil pan contents into the garbage and reuse the pan, which was only slightly stained at the bottom.