I have a York gas furnace and a Flotec condensate pump. The discharge tube travels vertically for 6’, horizontally for 12’, and then back down to a kitchen sink. Everything seems to work, except that the pump runs very frequently, and each time it pumps water up, it appears as though it all comes running back down into the pump. Is it possible to cut the tubing and install a check valve?

Not sure if a condensate pump can over come a check valve. If you try it let us know. I would extend the vertical run so it runs down hill to the sink. You will still have water running back into the pump, which is normal.