vacuum check valve ?
i had mine on the brake servo vacuum hose, which is just a hose from the brake servo to the inlet manifold, nothin in between
i think it might be the 2nd hose across from the drivers side, i think the first one is the vacuum hose for the map sensor
http://www.mbrunskill.pwp.blueyonder.co.uk/TB.jpg
right i think its the one the little hand is on, but have a feel around, its definitely not the one in the middle, and i think the one on the end is the Map sensor vacuum hose
BUT
as you can see on the diagram, the vacuum lines are offset to one side, and because of the design on the inlet manifold, any air the ecotek draws in will not be distributed equally, where the hose enters the I/M it has already started to break off to feed the air to each cylinder, at the most it will feed its swirly air to the 2 on the drivers side, therefore half of your engine will be running with more air than the other, this aint a good thing, everythin should be running equal
im a firm believer that the Ecotek works, but DONT use it on an RT, cos the design of the I/M means its not workin correctly for the car
take it off !