.Map :: MoHAA Mapping

I am making a map where players can go underwater in places, and I am not getting the bubble trails from gunshots like I have seen before. I have seen this in a brush using misc_outside/river texture for example. In my map I am using misc_outside/canal_sludge on a script_object entity (the water level is variable). Does any1 know why I am not getting bubble trails, and if it is possible to get them in the conditions I have? Any suggestions will be appreciated.

Does the bottom face of the brush have the water texture?

yes, all sides do. I get visual distortion that you normally get while under water and everything else seems right, just not the bubble trails.

Use no draw on all sides except the top and bottom