In l4d_vs_hospital03_sewers (Versus in Level 3 of the No Mercy Campaign), the fence directly opposite the gas station allows all but Tanks to climb it.
This has likely been an oversight since No Mercy was added, and actually became known to me when the "Taaannnkk!" mutation was first introduced. It's incredibly frustrating to go from absolute joy in that you get to be the Tank, to complete devastation when you realize you can't even get to the players.
If anyone knows a way we can get this to Valve, perhaps a little tweak is all that's needed to allow tanks to climb that particular fence. I do not know if this issue was prevalent in the original, so if someone could check that as well, that would be awesome.
EDIT: (This is an issue with the PC version-- I'm not entirely sure how it is on Linux machines.)
EDIT 2: Oops, forgot, screen shot for reference:http://steamcommunity.com/sharedfiles/filedetails/?id=230480247