Plugging the heater core

Somebody was talking about coolant gushing out of the hose in their engine bay, can't remember the thread.  Here's what you do with some rubber, chair leg stoppers would be the best, I think Mr Jim Arnett showed me that on a plug for the air filter.  I used pieces of hose before I read his suggestion.

Passenger's footwell on the left or the right side of the transmission hump.