There is a thread on renntech with instructions on a DIY slack tube thingy. I bought the parts and then fizzled out. I couldn't get my head around the diameter of the tube, to me (with my lack of physics) it seems the diameter is important, because with a bigger tube it seems like the water would move less, so I wouldn't trust the measurement. I guess except in a relative way.
Edit: Reading more about this, since the other end of the tube is open to atmosphere, maybe the diameter is not important. Hmmm... More research and education needed ... It is,always fun to learn something new
Here's the thread (registration required I think since it is a DIY)
http://www.renntech.org/forums/tutorials/article/255-an-inexpensive-way-to-test-for-a-bad-aos/
It links to this YouTube demo:
https://m.youtube.com/watch?ebc=ANyPxKpGJ-INErWCBGyqLs-cRz0sY78KHJCNxW1QbUGZy8iBmtqswG6AXnBWTJKo09Pd73bXu gu3Xb0ZZ2WTMPWeSqi-ud07xw&v=axBNu1CWJyY
Threaded Mode
