All my used medium goes through the seives over the lawn. The stuff retained by the seive is washed untill all the organic particles are removed, leaving just the stone component (whatever that is as I use so much different stuff). This is then chucked into a strong black plastic bag and placed out in a full sun position until I remember it

and then reused after 7 to 14 (or

) days.
I never reuse any thing, including pots, without some sort of sterilisation - hence the sun.