Comet really doesn't have a basement. His other restaurant Buck's, a few doors down, does. There's a Washington Post article from way back in 2013 that mentions this:
Like Pastan, James Alefantis, owner of Comet Ping Pong, doesn’t build his pizza sauce with DOP San Marzanos. For seven years, he has been buying late-harvest tomatoes from Toigo Orchards in Shippensburg, Pa., and canning them at nearby Stello Foods for use at Comet. Last year, Alefantis estimates, he bought 12 tons of Toigo tomatoes, which Stello turned into sauce and canned before trucking the jars to the basement at Buck’s Fishing & Camping, Alefantis’s other restaurant just a few steps down the block on Connecticut Avenue NW.
Comet really doesn't have a basement. His other restaurant Buck's, a few doors down, does. There's a Washington Post article from way back in 2013 that mentions this:
The Pegasus Museum. http://www.discerningthemystery.com/2018/12/james-alefantis-sends-death-threats-to.html?m=1