Our plumber installed a sheet metal drain pan for our 24" washer, with a drain connected at the back, through the floor. I think he had the pan made, I'm not sure. Our local code requires that the drain pan be drained to the outside, so it goes through a plastic pipe to the basement then through the outside wall. If you can get away with a plastic or metal pan with no drain, that's certainly cheaper and easier, but doesn't provide as much protection in an emergency. There's no water in ours (unless there should be a problem), so I'm not sure what someone is saying about smell. The washer drains into a standpipe.

Marita40, as far as preventing the sewer gas smell, you should do a search in this forum and in the plumbing forum on "trap primers".

It doesn't have to be attached to the sewer line. If an outside wall is readily attainable, it can simply drain that way.