There should be an inset in the wall for the washer hookups. The drain hose on the washer typically has a U at the top where it hooks into the house drain line. I imagine you could just stick the drain for the RO
down in there beside the washer hose. I wouldn't drill or cut into the washer drain line as it does have some pressure on it when the washer is pumping water out. Pull the washer drain hose out of the drain line, stick the RO
line in there, and stick the washer line back in...it should be snug enough to hold the RO
drain line in place. A couple of quick ties around both hoses would insure that the RO
drain didn't come out.