Dishwasher waste connection

Hi, i want to get a dishwasher but they all seem to require an air tight connection to the waste water, but currently i have an open pipe which i was going to hang the pipe into, the same height that my washing nachine is hung into a few feet along. I think this would be fine as i cant imagine the waste water from the dishwasher would come out any quicker than from the washing machine. Is there something im missing, or is this air tight connection just overkill to be safe?