Most people do not have a permanently installed darkroom space. If you are fortunate enough to own a house and can dedicate an entire room to printing, you are ahead of the game. However, like most of us, you are probably printing in a makeshift kitchen, bathroom or closet.
For those who can allot the space for it, a sink keeps all the mess in one permanently enclosed space. Inexpensive sinks are made of ABS plastic while high-end professional ones are made from quality steel. The ABS sinks work fine and will save you a lot of money. Stainless steel ones are much heavier and will neither stain nor warp.
There are many sink designs to choose from. Some have drains in the center, others have them off to one side, and others have no drain at all. Some have a standpipe that can be used to turn the sink into a water bath. You can also buy a temperature-regulated sink, which is a sink with a built-in thermometer. Backsplashes are normally not included with a sink and should be considered. Sinks must be plumbed in and unless you are familiar with basic premises of plumbing, the cost of a plumber must be factored in.
If possible, and if the space is there, it is best to get a sink that is bigger than you think you'll need. This is a case where bigger is better. An ideal sink should hold at least four or five trays of the largest size print you'll want to make (Develop/Stop/Fix/Hypo Clear/Holding Tray and Wash).
For people who cannot afford or have room for a regular sink, there is something called a Tray Ladder. A Tray Ladder is a rack on which you can stack several trays, much as you would find a file rack in an office. Tray Ladders are a good alternative for people who are working in a limited space. They are inexpensive when compared to a sink, save space but are harder to work with since the trays are stacked on top of each other. Necessary care must be taken when moving the paper from one tray to another.