Ok, im not quite sure what problem you are having, whether you cant group right, or if you cant get the sidechain to work. I assume your using FL7, so this is how i would do it.

Send kick to channel 1, send bass to channel 2. Click on channel one, then move the mouse over to channel 10, then right click on the send knob and select "Route to this channel only". Then click on channel 2 and do the same. Both channels will now be grouped to channel 10.

Now open a fruity peak controller on channel 1, and uncheck the mute button on the bottom right of the plugin. On channel 2, open a fruity balance. Right click on the volume knob of the fruity balance and select "Link to controller". In the internal controller section, select peak from the drop down. Now hit play. Go back to the fruity peak controller and change the settings on the controller to suit, To get a basic duck, set the far top left to nearly full, and the next one in to nearly off. Cant remember what they are called off the top of my head, one is called peak though.

You should now have a pump effect. You can now add compression to channel 10 aswell for extra effect.

Hope this helps.