In COLD Wisconsin! Our DWV on roof has been freezing shut so we have had to spray hot water on/in the pipe several times now to make sure it is still venting (at least a little). Had to do it this morning. This week the basement single basin sink and basement bathroom sink clogged. We used the baking soda vinegar trick on both sinks (overnight) and it appeared to work by the next morning but later in the day when we ran water in these sinks BASEMENT DISHWASHER clogged and overflowed onto the floor. Today we bought some drain cleaner and put it in both basement sinks. Later we started to run the UPSTRAIRS main dishwasher and it drained into both basement sinks! We also removed the septic pipe access cover in the basement to see if maybe it was frozen but there was some water in it and using a clog snake we couldn't find any blockage. I keep thinking the DWV problem has something to do with this but am otherwise at a loss on what is causing this or how to fix it! Please help! Thanx 
