I have a Bosch one (not sure of the model off the top of my head) but purchased from John Lewis 6 or so years ago which is plumbed in for the washer and the tumble dryer drains that way too.
It has never caused a problem, good wash cycles and works fairly well in terms of drying though I never feel the combined models dry as well as standalone dryers so if I needed a combined model again, I would buy something similar.