The bathtub is easier to use because it provides more room for pouring, but it comes with its own problems. Mop water can contain grit, hair, dirt, and cleaning products that may leave a ring around the tub, contribute to drain buildup, or potentially scratch delicate surfaces. A better choice is a deep utility or laundry sink, which is designed to handle messy household water and usually has a more suitable drain. If you have access to one, it should generally be your first choice for disposing of dirty mop water.
If you do not have a utility sink, the bathtub can still be used carefully. Place a mesh hair catcher over the drain to capture larger debris, pour the water slowly, and rinse the tub thoroughly afterward so dirt and cleaning residue do not remain behind. Be especially careful with the products used in your mop water. Never mix bleach with vinegar, ammonia, or other incompatible cleaners, because dangerous fumes can be produced. Cleaning products should always be used according to their labels rather than combined experimentally.
Another useful habit is to avoid carrying an extremely heavy bucket whenever possible. Spray mops, spin-mop systems, or simply using less water can reduce the strain involved in lifting and pouring dirty water. Mop water should also be replaced once it becomes visibly dirty or gray, because continuing to mop with heavily contaminated water may simply redistribute grime across the floor. The simplest rule is easy to remember: use a utility sink first, the bathtub when necessary, and the toilet only as a last resort.
