72. When washing clothes by hand, you need to apply soap thoroughly and rub it well, then wring it out. Of course, it's impossible to wring it completely dry. Assume that after wringing it out, 1 kilogram of water with dirt remains on the clothes. Now you have 18 kilograms of clean water. Assume that the water used for each rinse is a whole number of kilograms (assume that at the end of each rinse, the dirt is evenly distributed in the water). Question:
(1) If the clothes are rinsed twice, what is the minimum fraction of the original dirt that will remain?
(2) To make the residual dirt less than $\frac{1}{300}$ of the original, how many rinses are needed at least? Please provide a rinsing scheme that meets the condition and the reasoning behind it.