My '96 B22B1 auto wagon had a leaky radiator. I poured in some of that disgusting stop leaks stuff in it. Now when the engine's cooled down, the radiator hoses (which appear to be in good condition) collapse, as if there is a vacuum inside the system. I'm pretty sure that's not normal.

-What does this mean?
-What does that stop leaks gunk do?
-Is it harmful?
-Do I need to get my coolant flushed?
-Will its harmful effects be negated by a flush?
-Will my cooling system begin to leak again if flushed?

 

The Radiator Cap should allow coolant from the overflow bottle to return into the system as the engine cools.
The stop leak works by congealing when exposed to oxygen.
It might just be a matter of removing the radiator cap and cleaning the stop leak off, and you need to be sure the hose to the overflow bottle is clear of blockage.
you can prove out this problem by marking the coolant over flow bottle at the liquid level with a hot engine, then check the fluid level after the car has been sitting for several hours.