I just bought a new under-counter dishwasher that I plan to install myself. I am installing it in a room off the kitchen that already has plumbing and an existing drain for a washing machine. I want to tap the dishwasher drain tube into the existing washing machine drain pipe. The existing drain that I want to use is the typical plastic pipe that extends all the way through the roof to vent. The instructions only shows a diagram with the drain tube going into a disposal or sink drain pipe. The instructions say that the drain MUST connect above the trap in the drain. What am I losing by not using a trap? Thanks Jeremy

Question#1 A coming fall project is to replace the old iron water supply lines in my 130 year old house. The feed from the street is 3/4" and I was wondering if there is any advantage to continue the 3/4" throughout the cellar if the feed lines to the upper floors have already been done in 1/2" copper? A local hardware store employee suggested that a 3/4" line as far as the water heater might be advisable as it would reduce the temp change in the shower when a toilet is flushed. Question #2 Where the feed line from the street comes into the house, the first ten feet of line is in an small room in the cellar that is unheated. Last winter during a cold snap, the water pipe froze and I had to leave the door open and run a space heater to thaw the pipe. Luckily it did'nt burst! Would foam pipe insulation that wraps around the pipes keep it from doing the same this winter? Or do I have to heat an otherwise unused room all winter? Thanks in advance for any advise