How do I put a pvc pipe on a dehumidifier?

Use a piece of clear plastic tubing and two hose clamps. One end on the dehumidifier outlet and one on the PVC pipe.

You can find many diameter of clear tubing that you use on aquariums and aquarium pumps. They tend to not kink too badly. If you have a floor drain or shower stall nearby, run it to that drain and it will flow down from the dehumidifier into the drain by gravity and nothing will kink.

I used an old washing machine hose to connect to the back of my dehumidifier. It runs right into the sink now and I don't have to empty the bin. The washing machine hose has a connector on both ends. I cut off the connector on one end and hung it into the sink.

I have seen some folks use a section of garden hose screwed on, with the open end going down into a drain, but whether it would work for you or not, depends on your model of dehumidifier.