What's a good way to tell if a pool drain is actually working?

What's a good test of a pool drain (whether it's working or not)?
My pool is a bit complex, and, I'm trying to troubleshoot a poorly functioning (supposedly) self-cleaning system, and, one datapoint would be which of the 5 drains are working at any particular time.
I put my hands next to them, but I can't feel anything flowing. What's a good test?
Here, for the record, is a picture of the main drain (yellow) on the deep end and the main safety drain nearby on the wall (red): http://www.flickr.com/photos/98287134@N02/9330554473/
Here is a picture of a drain on the wall under one of the skimmers: http://www.flickr.com/photos/98287134@N02/9330560893/
And, here are two drains on the bottom of the spa: http://www.flickr.com/photos/98287134@N02/9330564727/
Given there are five drains, and three pumps (filter, cleaner, and spa), it behooves me to figure out which drains are actually working properly.
Hence the question: Q: How best can we tell whether a drain is working properly at any one point in time?
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On Sunday, July 21, 2013 2:28:27 AM UTC-4, Danny D. wrote:

I haven't done this, but it seems worth a try. Get an appropriate length of 1" PVC pipe and use it to pour a about a pint or so of water with blue food dye in it a couple of feet away from the drain.
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On Sun, 21 Jul 2013 06:28:27 +0000 (UTC), "Danny D."

Use food coloring in a small squeeze bottle. Squirt a little near the drain and see where it goes. That is the same trick you use to find pool leaks.
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On 7/21/2013 5:03 AM, snipped-for-privacy@aol.com wrote:

Yup. I've been told to use the Phenol reagent (the red stuff) but I think food color is probably a better idea.
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Yup. I've been told to use the Phenol reagent (the red stuff) but I think food color is probably a better idea.
Food coloring is supposed to be non-toxic, but maybe they just haven't trie d on enough people yet to be sure, or maybe they didn't give the test subje cts enough. Everything is toxic if used to excess. But food coloring seem s to me to be the safest, easiest, and cheapest way to go.
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On 7/20/2013 23:28, Danny D. wrote:

On a sunny day, gently enter the pool without stirring the water too much. If the circulation is adequate the temperature will be the same from the top to the bottom. For comparison try the same test when the pump has not been running that day. Water near the top will naturally be warmer than the bottom.
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On Sun, 21 Jul 2013 06:28:27 +0000, Danny D. wrote:

Thanks to your ideas, I ran a few experiments with the suggested food coloring near the 5 drains, 2 skimmers, 15 popups, & 6 jets.
http://farm3.staticflickr.com/2852/9401011955_ca7fb7a969_z.jpg
I found out what each of the 5 foot-wide drains do (3 floor and 2 wall drains) plus the two skimmers and the debris basket:
http://farm4.staticflickr.com/3820/9401012161_94dc5a7534_z.jpg
1. Floor drain (main drain, in the deep end) 2. Safety drain (on the deep-end wall near the floor drain) 3. Spa drain (main, one of two drains on the floor of the spa) 4. Spa safety (next to the floor drain of the spa) 5. Skimmer drain (on the wall just below skimmer 1)
Basically, the pool operates on two wholly separate circuits.
*FILTER CIRCUIT:* From main floor drain and secondary wall drain, to debris canister to filter pump to filter and back through four wall jets in the main pool and two wall jets in the spa and two always-on floor rotating pop-up squirters in the pool.
*SKIMMER CIRCUIT:* From skimmer 1 and skimmer 1 wall drain and skimmer 2 to skimmer (aka cleaner) pump to water valve 1 to water valve 2 to 15 rotating popup squirters, timed in series by the 9-port water valves.
I'm not sure which of the two floor drains in the spa is the main as they both suck water when the main filter pump is running. I assume they're 50:50 as there isn't any way to tell the difference other than they look slightly different.
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On Tue, 30 Jul 2013 19:52:37 +0000, Danny D. wrote:

I couldn't tell which of the two spa floor drains was the main and which was the safety though, as they both seemed to suck up dye equally:
http://farm4.staticflickr.com/3781/9208585061_e30dca9e19_o.jpg
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