There are a few fastidious folks out there who like to scrub out the inside of the WSM after each use, removing every bit of residue. Most of us don't, however. The residue won't contaminate your next cooking session. After a while, your WSM will smell more like smoke that any particular meat.
There are a couple of advantages to allowing the buildup to occur. Weber says the cooker will run up to 50*F hotter before the build-up reduces the reflectivity of the interior surfaces, so leaving the build-up helps the cooker run cooler. I think the build-up helps the lid seal against the cooking section a little better. Also, it helps minimize the moisture that sometimes runs down the inside of the unit and finds its way out around the access door knob and the charcoal bowl vents.
What I recommend before each use is to take a stiff bristle brush and remove any loose, flaking material from inside the lid, the lip where the lid meets the cooking section, the inside of the access door, and the inside of the cooking section.
If you notice during the course of the season that it looks like a lot of build-up wants to come off, just rinse with a garden hose and scrub with your stiff bristle brush. I had an experience last year where for some reason over 2 years of build-up just suddenly let loose, leaving the interior like new!
If you decide to use a cleaning product inside your WSM, I've heard good things about Simple Green and ZEP smokehouse cleaner (ZEP can be ordered from distributors found in the Yellow Pages).
There's a good section on cleanup and periodic maintenance items you can review on the
Usage Tips page.
By the way, Matt, how did your first experience turn out? What did you BBQ?
