Bucket , kitchen sink or dish washer . All have worked for me.
Simple green. , dawn and the special spray cleaners.
Oiling is recommended by the mfg.
The dust will destroy your rings .
I recommend oiling.
A day early or more is best.
Plenty have been done the day of , the engine acts a little funny for a while.
If you can, replace the air filter every time you come off the track...we always had about 6 filters ready to go...we sprayed oil on ours and curing time for that week and place them in a zip lock bag...as far for cleaning, simple green or purple power and let it soak then rinse off then blow them out with air
why put em in a zip lock bag?
I'll tell ya why. as they laying in the trailer or milk crate , the dirt and dust from going down the road gets on the inside of the filter.
learned quickly after traveling down a gravel road.