68 xr7 J-code with AC. Have new radiator ready to go in. Have flushed the engine twice until water ran clean while old radiator was still in place. In process of prepping to install new radiator and taking off old hoses, noticed what coolant was draining was STILL reddish-brown. Feel the need to flush some more b4 putting new radiator in for fear it may get clogged up. 133k miles and from what we have seen, do not believe cooling system was maintained AT ALL in its life!
There is an expanding bulb type drain cleaner that plumbers use. You hook a hose up to it and it expands to fit the inside of the pipe, then it seals and starts spraying water into the pipe. If you have a clog, this will then build pressure and force it down the pipe. To flush the engine block I took out the thermostat and put the thermostat housing back on the motor, stuck the bulb into the open end of the housing where the upper radiator hose would typically be and then turned the hose on full blast. This moved enough water through the block to actually get what looked like black sand to come out.
Hmm… what if your car is in the garage and you don’t want the “waste water” washing over everything as it drains out the bottom?
Mine is “garage bound” due to sloping driveway. So I can’t just roll it out and then roll it back inside :-/
My current plan is to reinstall the radiator and fill it all with fresh water, minus thermostat. Run the engine a bit to cycle the fluids, then drain and refill. Repeat as needed.
I got a tip a while ago to use some CLR in there as a “cleaning agent” when doing my poor man’s radiator flush. Not really sure how much / what ratio to use though - I imagine whatever the bottle says would suffice?
Hmm… maybe buy a sump pump drain hose and hook it up to the lower radiator hose connection and run it out the door? Sounds like a big mess to me.
Mike, how about taking an auger to your floor and drilling yourself a nice deep drain hole? 
Heh, I’ll bring that up with the boss 
All cooling system components new and car runs cool! THX all who lended help!
A really good way to ensure a clean motor is to remove the block drain plug. I also have removed the old freeze plugs. They are most likely steel and are rotting from the inside. Use the flushing T and away the junk goes! Replace w/ Dorman deep brass plugs. Easier to install than the thin ones!