Regarding Max flow problem ( Ford-Fulkerson Algorithm) I'm looking for the max flow in this graph but something is going wrong. 

First I take the path : 1-2-4-6. So the flow ie $F=1$
Then : 1-3-2-5-4-6 and the flow updates to $F=2+1=3$
If i take the path : 1-3-5-6 my flow is $F=3+2=5$ 
And the graph is disconnected now. I can't  reach 6 starting in 1. I know the maximum flow should be 6 but I think the algorithm stops when there's not path joining the source and the target.
What's the extra condition I'm missing? How can i find the maximum flow?

There are two flows,
1) forward flow (directed edge)
2) reverse flow (opposite to edge direction)
0 <= forward flow - reverse flow <= capacity of edge

so in residual network, there will be reverse capacity available for every forward flow
available reverse capacity = forward flow - reverse flow

In above case, there is reverse capacity of 2 available from node (2) to node (3), so there is one more path possible 1->2->3->5->6 F = 5 + 1 = 6.
