That's an excellent and very important question. The short and critical answer is no, you should absolutely never use a standard plastic or rubber outdoor trash can for hot ashes from your grill, fireplace, or fire pit. This is one of the most common and dangerous mistakes homeowners make, and it poses a severe fire risk.
Hot ashes can retain intense heat for hours or even days after a fire seems out. When placed in a standard trash can, these embers can smolder undetected. The plastic liner or the can itself can melt, ignite, and quickly lead to a full-blown fire. This can spread to your home, garage, or nearby structures, causing devastating damage.
For safe disposal, you must use a dedicated, non-combustible metal ash can with a tight-fitting lid, placed on a non-flammable surface like dirt or concrete, away from your home and any flammable materials. Always let ashes cool for at least 48-72 hours before even considering disposal. When in doubt, wait longer or mix them with water thoroughly. Your safety and property are worth the extra caution.