I have an ash catcher attached to the charcoal basket on both of my UDSs. now. On my old UDS, which didn't have anything to catch ashes/grease, i would simply take the basket and racks out and dump everything out.
I'm afraid that washing/rinsing will effect the seasoning of the smoker. Maybe not.
IMBAS Certified MOINK Ball maker and IMBAS Sgt. At Arms.
And now, brethren, I commend you to God, and to the word of his grace, which is able to build you up, and to give you an inheritance among all them which are sanctified. [Acts 20:32 KJV]