[Users] failure route doubts

Hi, I'm having some doubts on how to use/do some things with dispatcher module and failure route. I'll try to explain my problem. On my main route block I select the destination (using ds_select_dst) to where I want to send the message, and indicate that responses should pass through the failure_route, I also add a header with some things that are needed by the next proxy. On the failure route when I get 408 Time Out I mark the previous destination and select the next destination. until here everything goes fine. After this I want to change the message that I'm going to send to next proxy, for this I need to remove the header that I inserted previously on the main route block and access the destination URI that the ds_next_dst updates. My first doubt is that when I print the destination URI it has the previous destination ( the one used in the main route block) but when it relay's the message it goes to the right destination (the one returned from ds_next_dst), Is there any reason for this ? I'm using $du to access it, is this wrong? My second doubt is, what sip message do I have access to in the failure route (the one I received or the one I sent out)? I ask this because I try to remove the header I inserted in the main route block and it does not remove anything but when I relay the message the header I tried to remove goes on the message. Thanks in advance, José Carlos Silva