A crack in my foundation wall is leaking
Doing that will be virtually useless.  It may help when there is very very light water pressure for a little bit.  However note that by stopping the water from coming in temporarily that it will work harder on the cracked area.  

Which means that the crack will grow larger faster and soon leak again.  You need to fill the crack with some type of concrete patching compound plus waterproofing (the outside) or what is usually the best method is chiseling out the cracked area and adding an epoxy to secure it.  

Both of these methods have products that allow them to be done when wet however they are cheaper and more effective when completely dry.  There are epoxy kits that you can get for abut $200-300 in the US.  It is borderline DIY.  If you have things that you are trying to protect in your basement I would probably call a professional which isn't a whole lot more than the kit.