I have a 1" drain on mine and works just fine. I'm primarily cooking whole hogs so I know all about grease build up. All I do is crack the valve while cooking at least once to get rid of the majority. This keeps the sludge down a little. I still have to scrape the baffle plate to keep it from crusting up. Try draining yours at least once during your cook while it's all hot and flows smooth and see it it helps you.
My point is that there is nothing to drain. The whole point of a reverse flow is getting the drippings to vaporize on the baffle plate. This adds moisture and flavor in my opinion and eliminates the need for a water pan. The crusties scrape up easily and I’m left with very little grease to dispose of or mess with.
A whole hog may be a different story, never done one.
And yes, 50 pounds of raw whole chicken cooks down to about 22 pounds of pulled meat. It was nicely vacuum sealed in half pound bags and will, along with some homemade bacon, make some nice holiday gifts for friends this year.