Ro/di water, and i use reef crystals. I have 3 brute cans that all smell like it. One for fresh ro/di storage, another for mixing and one for waste water
Yes i do clean them out periodically. More so my mixing can to clean the residue out etc. And yes, the can that holds waste water only has the same smell to it.
I'm now putting my ro/di and pre-mixed saltwater in food grade five gallon buckets that they sell at Lowe's. The lid has a rubber gasket in it. No smell with these buckets.
This is what I may move to for stoarge as 5g isn't enough for me.
http://www.plastic-mart.com/category/109/plastic-storage-tanks
Here's a good thread with a lot of ideas on water mixing and storage.
http://www.reefcentral.com/forums/showthread.php?t=1711626&highlight=water+change+container