On my 240D the T fitting of the backflush system is set in the hose running to the heater core in front of the intake manifold on right side of the engine - dont loose the rubber gasket that fits under the cap. And it can easily be moved and temporarily set on left side where heater core return hose goes to cyl.head.... you just set it on end of the hose and hold your thumb over the open end...... first douching the heater core, then setting it on other side of the hose to purge the cyl head galleries.

I like the valvoline 6-8 hr. flush that you use when driving....... the 30 min. stuff seems too good to be true. Prestone Orange in silver plastic jug is what I use for coolant. Maybe get yerself one of those $3 bubble tube coolant test tubes too.... you know the one that floats plastic bubbles.... I keep mine wedged in front of the radiator...... have also got tools, nuts 'n bolts cached in small bucket behind the w/w washer tank.

Its actually a fine hot, Summer day operation flushing the radiator.... so you may wanna let the pros do it this time with not much time between now and Sunday. No doubt the car will love the 4-5 hour drive and run better for having made the trip.