Looked for the scene in season 4 and couldn't find it.
at me for thinking it was on season 4. Anyway, went to the second episode of the 5th season and saw this:
I BELIEVE Walt is throwing away the ricin via the toilet.
Then Walt proceeds to tape what is either salt (why would he put salt behind wall socket?) or the Lily of the Valley berries on the back of the wall socket.
So Walt is either putting salt behind Jessie's wall socket (why would he do this?); the Lily of the Valley berries behind Jessie's wall socket (why would he do this? He COULD lose the trust of his partner if Jesse has some electrical problems and has to open said wall socket and finds the Lily of Valley berries planted); or the Lily of the Valley berries behind HIS (to use later on - but why? Brock survived from it so what real use does it have killing a target) wall socket.
Edit: Nevermind, did some more research and found out that ricin comes in the form of white powder. I was confused because the ricin Walt gave Jesse was brown/dark brown. So I guess I can assume that Walt produced more ricin. Probably threw away the brown ricin in the toilet Saul got from Huell and produced a newer white version of the poison. Googled "can ricin expire" and didn't get any answers (only looked at the first page though). Confused me 'cause the Lily of the Valley flowers are white, too. So I guess the real question is, why would Walt want to produce a white version of ricin?