I have a sump pump discharging through a 1 1/2" PVC line to a drainage swail, about 80' run. I have a check valve installed immediately after the pump to prevent the line from siphoning back into the well at the end of the pump cycle. To prevent freezing (we are in upstate New York) I have had to drill a 1/8" hole at the top of the discharge line to break the vacuum and allow the line to drain after each pump cycle. Although this works well, indicating the drainage line has proper pitch, it is a problem in that the small amount of water that comes out of the 1/8" hole, over a period of several days in sub freezing weather, forms enough ice to start to block the hole.
I am thinking that what is needed is some sort of a vacuum relief valve, installed on the inside of the house to avoid freeze up issues, to break the vacuum and allow the line to drain. I have been to several local plumbing supply houses, and they have been of no assistance. Any thoughts other than replacing the 1 1/2 line with a 3 or 4 inch line and letting the 1 1/2 dishcarge line break vacuum where the two lines meet?