Your darkroom can be any area that can be temporarily made dark - no light leakage. The ultimate is to build yourself a permanent darkroom that is not used for anything else. It is not a luxury if this is to be your hobby. The room can be as elaborate, or as plain as you desire.

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You can use a bathroom, laundry room, or utility room as a temporary darkroom. It is always nice, but not necessary to have running water and a drain in the room. If you decide to use your bathroom and have a family, a little scheduling might be required or you might have a family accident.

Making a room temporarily light tight is not as easy as you might think. You can cover the windows with aluminum foil or other light proof material, but it must be held securely in place. If you use tape there is always the danger that you might pull the paint off of the wall. Then you have the problem of sealing around the door and I mean all around the door, not just underneath. You also have the possibility of chemical spills, which could stain the flooring. In my opinion the setup and cleanup times for a temporary darkroom make the whole process just too much of a waste of time, but of course the choice is yours - I realize that not everyone has the space and money for a permanent darkroom.

Test to see if your darkroom is light tight
If after 5 minutes in total darkness, you cannot see your hand in front of your face, then it should be safe for processing your films and paper.
A more exacting test is to leave a small strip of photographic paper in the room for 5 minutes and then process the strip for the recommended times in your developer, stop bath and fixer solutions. Wash and dry the strip as you would a normal print. Then compare the strip to a piece of undeveloped paper in daylight (this will destroy the undeveloped piece of course) - if you cannot see any difference, then you have a light tight set up.