This first step of the argument for impropriety is obviously demonstrably absolute nonsense. The reason is that there are independent groups which attempt to detect charities which aren't really charities. As far as I know, they all give the Clinton foundation their highest rating.
Charity Watch rates it A and notes that (I think for different years) 88% & 89% of the money goes to the stated purposes. That's not 100%, but they also note that the average for good charities is more like 75%. Daniel Borochoff (president of Charity Watch) described the Clinton foundation as "outstanding"
Charity Navigator gives The Clinton Foundation four stars (the maximum rating). In contrast it give the American Red Cross three stars. Guide Star rates it Platinum (don't search for Platinum :-( the rating is a *.jpg in the upper right corner of the page).
This is not a slush fund.
I have a theory for why I read so many articles questioning the integrity of the operations of the Clinton Foundation. I think the Clintons are being punished for insisting (in this case) on transparency. Although not required to do so, the Clinton Foundation publishes a searchable list of donors. This makes it relatively easy to check for donors who met Clinton when she was secretary of state (not easy as State resisted releasing her calanders but easier than looking for meetings with people who paid her to speak).
So journalists (who worked very hard on the stories) looked for corruption where it was easier to check, found none, and wrote lede paragraphs suggesting they have maybe found the shadow of a possible appearance of conflict of interest (then someone wrote a headline damaging to the Clintons and also AP wrote and refused to correct an absolutely false libelous tweet).
Now political journalists talk and write about how Clinton is hurt by "questions", that is the media report on the choices of the media and their effects. Of course the misleading headlines and ledes hurt Clinton. Most people don't have time to read the stories and notice that they provide strong evidence that the Clintons (and Abedine) have been very very careful to avoid anything which might even be alleged to appear to be ethically questionable.
Now I'd guess that any of the few readers of this blog know all this, so why am I typing it ? Yes you guessed, I've had twitter debates (which I can't find in my time line because at least twitter doesn't make that easy)
American Red Cross has had it's share of real scandals.
Someone else said the Clinton Foundation spent it's money on, in effect, luxurious consumption (junkets fancy meals at meetings) & noted the true but irrelevant fact that it gives only 10% of its revenues to other charities. I said they spend most of their money on direct assistance to poor people. My twitter correspondent said I couldn't know that as their accounts are secret. I admitted (only to myself) that it was something I vaguely remember reading on the web somewhere at a place I trusted. Obviously, as noted by Charity Watch for example, the accounts aren't secret and most of the money is spent on direct aid to poor people.
Anyway, these cases show it isn't just journalists who assume that the Clinton's just must be corrupt.