You guys/gals are SO HELPFUL it's crazy! we had a well guy out a few months ago and I will look up the paperwork, he should have the psi listed on that.It is not a ton of waste but it will be 3 to 4 times the amount of RO/DI you make. You probably send more down the drain from the toilet and a couple showers than it will produce in a months time. The drain recharges the groundwater supply so not a bad option really.
You could also run the waste line outside in warmer months and water the garden or landscape as long as you prop the end up so it cannot suck anything back in the line.
Something you need to keep in mind is it takes a minimum of 40 psi to operate a RO system and often domestic well systems are set to operate at around 35 psi. You may need a RO booster pump, which is much cheaper to operate thay trying to adjust your well systems pressure switch up. RO membranes become more efficient the higher the pressure is, I run my booster pump at 95-100 psi.
