So you want to spew like the pros. Or, at the very least, the idiots in our band. Before our last tour with GWAR, we rejiggered our entire system of blood delivery. Based on a system devised by Sean, I made a revised version of a self contained blood tank that could send pressurized spew to the wanting masses.
Sean first got the idea to use plastic pipes for self-contained blood spewing some years back. It involved sealing and pressurizing plastic tubes with common Schraeder bike pump valves. Everything was customized for each individual costume, though, and require fragile gravity feeds. Years later, I came up with this diagram after thinking about how a spray bottle worked: