Thinners damped rag, then tyre black. It won't hurt the rubber if you're quick about it and use just a damped rag. How long ago did you paint it? You're not lazy at all - it'll take much longer to clean the tyres than it would have taken to drape a sheet over them.
Yey - looks like a bus now. I know you've had your hold-ups - wasn't sure you'd get back on this for a while but it's great to see you've got it painted. But yellow? You must love your missus...
I'll get some nice outside shots when I take it out to clean it, need them for the ins company anyway. Oh, it passed by the way!!