To Be Specific:
Its a material from hl2 (Half Life 2)
Used in the the HL2 Episodes and Portal.
You should have it, if you have Portal or episodes of HL2.

Well my portal and portal 2 folders are in seperate dierectories, but I checked both and I still don't see this source material gcf.

go into Program Files or Program Files(x86)/ Steam / steamapps / source materials.gcf

Ok well, I know I shouldn't say this because it is going to ruin the feeling of the map when your escaping but it seems to be the only solution. I have tried every toxic slime texture that Hammer gives you and none of them work. So after an hour of searching through all the textures I came across the skybox texture. Got an idea. And covered the whole map with a blue water color of skybox texture. Then I switched it from a func_detail to a func_illusionary, to keep it so you can't land on it nor put a portal on it, and it works!! Not very threatening like toxic slime but it does the trick. Next time when I make a huge ass map, I will have to remember to put the slime in before hand. So I believe the problem is fixed and thanks once-once-again for offering ideas on how to fix this stupid issue.