I agree, the fake blood will be too thick. It'll be cheaper to do the colored water also. The fake blood is done with corn syrups so it will congeal a little to stay in place (once exposed to air).

You're gonna want the wall blood to flow, the fake blood just isn't gonna do it.

The other issue you will have is your painter tarp will need to be white or the colored water will lose it's effect (look brown or black). Try buying some tonic water and add red food color, add a black light (tonic glows under black light) and see if it will glow under the light...if this works it might be a cool effect.

Good luck and lets us know how it works and of course pictures!

Don't let people drive you insane when you know it's within walking distance.