I have my RO in my shed at the end of my 60 foot garden. The tank is next to it, but the waste travels under my garden and into my drain. The point this makes is that it doesn't matter too much how far the waste travels. So find some way of getting to drain, under the floorboards and along to some pipe somewhere, connect to the rear of a sink? Under the floorboards to the kitchen maybe?
I knew one guy who dug a dirty great hole he said 10 foot deep and bury the waste pipe there. below the foundations etc and it was fine. Personally I'd prefer to find a way to connect to the drainage system