With regard to the Islamically prescribed manner of washing the deceased:
It begins first of all with istinja’ (washing the private parts), if any urine or stools have been expelled. The washer should place a cloth over his hand and wash away any dirt from the back and front passage, pouring water over it. He should also cover the area between the navel and the knees so that it cannot be seen. After that, he should do wudoo’ for the deceased, wiping the mouth and nose with water, washing the face and arms, wiping the head and ears, and washing the feet. Then he should pour water containing lotus leaves over the head, then over the right side, then over the left side, then pour water all over the body. In the final washing he should add camphor to the water, which is a well-known perfume that strengthens the body and gives a pleasant fragrance.
This is the best way, but any manner of washing is acceptable. What matters is that water should reach the entire body and remove any dirt.
But the best way is to start with istinja’ (cleaning the private parts), then wudoo’, then washing the body with water and lotus leaves three times, then pouring water over the body, three times on the right side and three times on the left. If there is a need to do that more than three times, then it should be five times; if there is a need for more than that, then it should be seven times. It should be an odd number of times; this is preferable.
But if the person is washed once or twice, that is acceptable, although what is preferred is three or five or seven times, if need be.
And Allah knows best.
(Source - Islam Q&A)