If your bathtub drains quite slowly, it's probably stopped up with stuff. You can try using Mr. Plumber, squirt some into the drain and wait fifteen minutes then flush with water.  There's no need at all to be afraid it will damage the drain pipes.
如果沖涼缸去水好慢，可能係塞咗嘢㗎，你試吓用通渠佬，唧落去等十五分鐘再沖水，都唔使怕影響啲喉管。