and what if they wanted to blow up multiple planes on the same day through timed devices placed months ahead of time in the septic tanks of planes? How many people would that take so they could go plane to plane to plane?
If they want to do that, why not just get some people hired to work as baggage handlers? On the day in question, just throw the explosives into one of the air cargo containers and be done with it.
I don't buy your idea simply because there are way too many things that could go wrong. First off, how would the explosives and detonators react in a caustic environment? They would also need to know airline procedures for how the 'septic tank' is maintained, etc.. If they have access to that, they have access to better ways to do it and wouldn't need to go through a wondering musician parade on the plane.
How do airliners dump toilet waste?
Seems to me to put the final nail in the coffin of this bathroom theory.