In theory the job is easy but there are things that need to be considered. First of all, the current raw water wash-down pump may or may not be rated for continuous duty. The worst that would happen is that it would overheat but it probably it won't do that. Continuous use may lead to shorter life though. The second and more important consideration is the gallon per minute rating of the pump. It should be matched to the size of your live well to provide the appropriate number of water changes per hour. For a 30 gal tank as an example, you need a pump rated at about 10 GPM or so. Your pail may be smaller so a smaller pump is OK.
The existing wash down would feed the tank. The tank(pail) would have a cutout, fitting and a hose somewhere near the top for overflow and a drain at the bottom to empty the tank. Of course you could eliminate the drain and just dump the tank when finished using it. The overflow can drain onto the deck or over the side.
One thing to be aware of is that the tank will be heavy when full and unless lashed down could fly about.
