This thread should be posted in the detailing forum.
I think for the interior, less is more. Just get yourself some white wash clothes and some clean warm water. This is all you need for regular upkeep. You are basically dusting your interior.
If you have a filthy interior, then you can use a more agressive approach. Some soap suds from your wash bucket and a brush with some good bristles will do the trick for loosening the ground in soil. Follow with the clean towel to pick up the suds and dirt.
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