Do your best to clean it out. Sometimes I get lazy and put it off for a few days after a cook, but its my understanding that ash + moisture can lead to the ceramic lining eating away.
WSM 22 ~ WSM 18 ~ Maverick ET-732 ~ Flaming Fast Thermapen ~ Weber SS Performer ~ Weber 22 OTS ~ Weber 22 OTS ~ Weber 22 OTPlus ~ Weber 22 OTS ~ Weber Q300
When all else fails just ask yourself, WWGALD???