I am getting ready to install a Weil-Mclain Ultra in my 4 family apartment buliding. It stesses how important it is to flush any sediment out of the lines. Here is where my problem comes in. The system was once a gravity feed system (building was built in 1939) most lines are 3" and I have drained the whole system and was really suprised at the amount of water it held. I don't think by just running water through it will be enough to dislodge any sediment as it will have to fill all the lower lines till it reaches the top and comes back down. Should I just fill er' up and hope for the best? I guess I will dismatle the heat exchanger and try to remove any deposits in the spring. If any body has any ideas please let me know.