I’ve been trying to find a solution to create an intermittent inflow for a fluid sim, (I.e. Using an old water pump), and finally came up with a solution: Use location keyframes to animate the inflow object. Whenever the inflow object leaves the domain, the flow stops.
This means if you want a character violently shaking a ketchup bottle, you could constrain the inflow object to the tip of the ketchup nozzle, so every time the nozzle enters the fluid sim domain object, it will release a stream of liquid that stops as soon as the object leaves the domain. Be sure to set the other objects in the domain to be splattered as obstructions.
You can also use this to control the flow volume over time: A tapered object, such as a cone, will create a small inflow when the tip intersects the domain, and a much stronger flow as the broader base is added. So a character turning on a faucet can start with a slight trickle, and build to a flood through the scene.
There are limits to this; a character with a gushing artery couldn’t stand in the middle of a room-sized domain, but if the bleeding part is along the edge of a domain, then the control object could piston in and out of that domain edge to create a spurting effect.
Anyway, I’m sure others have figured this out, but I haven’t seen a solution to this anywhere before. I figured I might as well share in case anyone else had this frustration.