Installation as is, meets requirements, although not ideal. There may be some backflow from the sink into the Standpipe trap, but if machine is in frequent use, that will soon get washed through to the drain. Problem may actually be lack of use of the sink, try running some water down it once a week and see if things improve.
I would also though cap the existing connection from the Standpipe with a Cleaning eye, and Tee the washing machine waste in just above the Tee, into the vertical pipe, cut the standpipe down slightly to suit. I'd also fit a couple of clips to secure the standpipe to the cupboard using 3/8" woodscrews.
I would also though cap the existing connection from the Standpipe with a Cleaning eye, and Tee the washing machine waste in just above the Tee, into the vertical pipe, cut the standpipe down slightly to suit. I'd also fit a couple of clips to secure the standpipe to the cupboard using 3/8" woodscrews.
