I have a very humid basement, in which I run a dehumidifier often. To allow for a more constant run, I purchased a dehumidifier pump. It says to run the pump out through a window or to a sink. I don't have a sink and I am worried about using the window in the winter (freezing, etc.). My question is, Is there a way I could use the standpipe that my washer drain goes into? It is in relatively good proximity to where I would be setting up the dehumidifier.
Yes, there should be no problem with doing that, provided you're within distance constraints of the pump. The washer stand pipe should just be a vertical pipe, with your washer drain going inside it, and not actually connected/sealed. This is done so that there is a vacuum break. You should simply put the pipe from this pump along side the washer pipe in the same way - do not attach it with fittings, otherwise you risk water from the pump going into your washer, or more likely, drain water from the washer going into the pump.
In this picture, the white pipe is the standpipe, the black is the drain connected to the washer.
Basically, just put the pipe from your dehumidifier pump alongside the black pipe.
To echo @Jeff Widmer, you may want to tie the pipes down afterwards (a zip tie or some electrical tape around the whole thing may work), just to be sure neither pipe ever slips out and sprays everywhere. Again, don't seal this up or use fittings - you specifically need an air gap.
I don't see why not: if you run it to a sink, it's going to go down the drain to a pipe which runs to your sewer or septic line, same as your washer.
To prevent water from the washer from backing up inside the hose from the pump, you'd need to make sure that the hose feeds downward before entering the washer's drainpipe, so at the very least you should mount the hose so that there's a few feet of vertical drop above where you connect it.
Our house has a pump to move the AC condensate, the washer stand pipe has a t/y so that the washer goes into the side and then the pipe continues up for a foot or so and then the discharge from the pump drops in the top. Also, the discharge pipe is slightly above the top of the standpipe to leave an air gap.
The discharge from ours is a thin flexible copper pipe, so we don't have any thing tying it down, but if yours is plastic you probably want to attach it somehow, just so it doesn't fall over and spill water on the floor. You should maintain an air gap, but honestly, if you go the t/y route, the entrance the washer uses will provide an opening that water can't rise above.
Is there not a floor drain in the basement? Typically all basements will have a floor drain in case there is any water. Most of the time the furnace will drain into this. Where does your furnace drain to today?
Sometimes this basement floor drain will then go to a sump pump, to be carried out of the house.