Here is a simple solution to getting random flow. This design can be scaled down or up depending on need but for simplicity sake I used 1/2" pvc.
The material used:
1/2" pvc pipe (drilled)
1/2" pvc end-cap
3/4" pvc end-cap (slotted)
Basically you take the 3/4" end-cap and cut angled slots in the cap such that when water is forced through the slots it will spin the cap. The more slots you make the slower the rpms. I designed 2 different caps. One with 2 slots and one with 10 slots. Connecting the pipe to my kitchen sink I was getting ~70 rpm out of the 2 slot cap. The 10 slot spun much much slower. Then cut a hole out of the top of the cap so it will slide over the 1/2" pvc pipe and spin freely.
Take the 1/2" end-cap and place it over the 1/2" pvc pipe. Then drill or cut holes in the pipe directly above the cap. Cut these holes rather large, you do not want to limit the flow of water here. That is what the angled slots are for.
Here is the slotted cap, notice the angled slots.
Here is the pipe, notice the large holes directly above the cap.
It is "assembled" here. Basically you slide the 3/4" cap over the drilled holes. The water will exit the pipe and then exit through the angled slots spinning the cap. When the cap spins it will direct the flow of water around the pipe creating random flow.
This is a very simple design that should work for most systems. It could be scaled down and run by a smaller pump also.
To create the angled slots and other holes I simply used a dremel with a small disc style grinder it worked very well.
I'm open to suggestions, comments, and improvements. I just hope I helped someone out.