307 Purge Cannister

[walcit]

I was just wondering about this on my 307. The garage says it needs renewing because of an antipollution fault. The wheel arch liner did come off (now it's been replaced). I took the cannister off the other day and found that it had two pipes going into it (one from tank the other to engine) and an elec connection. Also there was a big hole on the other side - it lloked like there should be another pipe on there or that there should be a cap on it? Could anyone tell me if there should be a an open end on one end of the cannister? It doesnt make sense to me that there should be. Please could anyone advise?

Thanks