On Mon, 5 Sep 2011 10:21:41 -0700 (PDT), wrote:

you should have water flowing at the
pool pad if you just open a fitting, like the pump
skimmer basket.

Yes. If I forget to shut off the valves at the pool pad, then, whenever I
open any of the three pump filter baskets at the pad, water flows forever
until I realize it and shut off the valves.

And since I think you said the
suction from the pool is only the bottom drain
and a side fitting, by plugging up that side
fitting you could determine if the bottom drain
if flowing or not.

You must be an engineer! That's an elegant diagnostic!

1. I would set the valves at the pool pad to only allow input water from
the pool (and not from the spa).

2. I would cover just the safety drain at the side of the deep end of the
pool (leaving the main drain at the bottom of the deep end of the pool
alone).

3. Then, if I open the pump filter basket, water should flow if the bottom
drain is unclogged.

Very elegant. I suspect a plastic bag should work on the side filter to
plug it up.