Repro guys at the vet school told me that there's enough progesterone in the ones marketed in the USA for two uses; that's what we do with them. Kris, if you're getting 3 rounds out of 'em, good for you - but I'll just pitch mine after the second round.
They told us to just rinse/scrub 'em with water - no soap, as it can remove some of the progesterone. Sometimes I'll run 'em through the dishwasher on a short cycle without any detergent. A dip in Nolvasan is probably in order, as we've had some develop a pretty funky vaginitis - and I've seen a report that using Nolvalube(OB lube with Nolvasan in it) to lube 'em up at insertion can lead to increased conception rates, as it diminishes the incidence of vaginitis.
I have access to a large autoclave at work, so usually autoclave the cleaned, used CIDRs - and supposedly, autoclaving 'brings more progesterone to the surface'.