If I clean at all I agree with Nun Hunter. Lyman or, just bought from here RCBS, tumbler and walnut granules.
I don't decap before tumbling but do it afterwards to be sure I've no granule in the flas holes.
My thought is it's only the outside of the case that benefits from cleaning in making it look nicer when it's been sized.
On really, really, really dirty cases I used the liquid cleaning solution that you soaked them in for some time (as per instructions).
Then immediately rinsed in two separate waters.
A pre-rinse then a final rinse. As these cleaning solutions would leech the zinc if left too long or not fully rinsed.