Here's what I do ...
Before leaving the house fill the livewell with clean water and add your chemical (see below), drive to your fishing spot and drain before launching - now launch and start your pump to cycle and clean - it will be ready for fish within the hour. By adding nice clean water at the house and driving - you get a nice sloshing that will clean her up well. Don't worry if a bit gets out, it won't hurt a thing as long as you stick to bilge cleaner and/or baking soda.
If it is extra dirty, slimy, etc. - use bilge cleaner. It is biodegradable and non-toxic.
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If it is just a bit smelly and needs sprucing up - use baking soda. It won't hurt a thing, either.
The trick is to do this once a month or more often, keeps it from getting too bad.
Hope that helps.