I was told if you try sending it into the sewer through a nearby cleanout (I have one), that there is a possibility of sewage backing up into the building. The waste lines at a residence might not be able to handle the flow--they're not really designed for that. In my neighborhood, we shouldn't dump to the street storm drain because it sometimes goes straight into the Bay. I was told to install a "blow-down pit." Now we have a cartridge filter and just bought new cartridges and there is no backwashing involved.

I do have a brass ball-valve on my equipment that diverts a small amount of water for draining purposes. It is installed between the heater and the filter. If you use a cartridge filter, that is an option....