The pool and the spa both have multiple drains in them, I assumed to reduce the entrapment risk. If that's not enough then I guess I'll have to put just a little more priority on this project I am considering.

I dug up the pipe under the "strange contraption" which it turns out is a spring check valve (that must not be closing correctly). Unfortunately, it looks like the underground section of pipe for the spa is also 1.5" .

Are the jets themselves something that can be accessed from the spa end of the pipe, or is that something that would require breaking up the decking to access?