I don't know exactly what "gasket" you are talking about, as the only thing I can imagine is a slide out seal, which is black rubber on my TT. If you are referring to rubber slide out seals, I'd be reluctant to use harsh cleaners or chlorine on them, since you need the seals to remain supple. I wash mine with soapy water when I'm washing my TT, and use "slide out conditioner" (available from Camping World) a couple of times each season to attempt to condition and maintain the seal.
2013 Windjammer 3008W
2006 Chevy Silverado 2500HD 6.0L w/Equalizer 4
Nights camped: 2012 (29); 2013 (26); 2014 (40); 2015 (43); 2016 (35)