As a rule, a Blessing on a Mitzva must be recited before the Mitzva is done. It cannot be made after the Mitzva. This is true by almost all Mitzvos. Why do we recite the Bracha on the washing of hands before washing?
The explanation is as follows. Since our hands may have touched something that will prohibit us from reciting the blessing, we have no choice but to make the blessing after the washing.
Rabbeinu Yeruchum writes that we should recite the Bracha after washing each hand one time, and recite the Bracha before pouring water on them for the second time, but this is not the accepted custom.
Rama explains a bit differently. Since the drying of our hands is part of the washing, even though our hands have already been washed, the Mitzva has not been completed. It is therefore considered as if we are washing before the Mitzva is done.
Based on this Rama, Mishna Berura points out that it is important to recite the blessing before we dry our hands.
Two important rules come out from this discussion.
1 If one dried his hands before reciting the blessing of Al Netilas Yadayim, there are some who say the Bracha can no longer be recited.
2 One cannot interrupt after the washing, before drying, with trivialities, as the drying is considered part of the washing.
One is required to wash hands from a receptacle. The receptacle can be made from any material. There is a discussion among the contemporary Poskim regarding the use of a disposable cup for washing. Reb Moshe Feinstein seems to say that it would suffice for washing hands, although it is best not to use for Kiddush.
The cup must be large enough to hold a Reviis of water. A Reviis is between 3.3 and 5.2 ounces. Being that it is difficult to wash properly with so little water, it is recommended to use a cup that is larger.
If there is a hole in the cup that is large enough for water to drip out of, the cup cannot be used. If the hole is higher up on the vessel, in a place where the cup can still hold a Reviis of water, there is a difference of opinion if we view the cup as broken, and it cannot be used, or we say that it is considered useful below the hole, and it can therefore be used for washing. Bais Yosef rules that it can be used, whereas the Magen Avrohom and Vilna Goan, along with others rule that it cannot be used.
Interestingly, if the hole is large enough that water can be poured from it, we view the hole as an opening, and it can be used for washing.