Winterised ours in 2019, and never used at all due to pandemic in 2020. So lasted 2 years. This year only used in our province for 12 nights sadly so we didn't dewinterise the washer/dryer. All was well for the 2 years but this year we did run more antifreeze (year 3) through the washer as well of course winterise everything else and pour down pee traps.
Put plenty in your toilet for the seal and cover the bowl with Saran Wrap to avoid drying out too quickly, and all should be good. If you feel uncomfortable though just flush through with more AF this year and of course all U bends/traps.