Depends on where it has been kept and abuse suffered (scouring) I have had mine over 15 years, kept out of sunlight. I have 2 15 litre ones which dispenses nutrient for hydroponics the lids cracked after 2 years so I am not expecting the vessels to last much longer.I have an aging (~ 30 years old) 25L plastic fermenting pail.
How often would you replace it with a new one, considering that plastic degrades over time ?