Is your boat equipped with a macerator pump? If yes there is a Y valve that must be switched to overboard discharge then you press both rocker switches at the same time to discharge the holding tank. The reason for two switches is so you cannot accidently discharge. Maxum put the switches on its cruisers standard even if not equipped with a macerator they just aren't wired to anything.
1997 2400 SCR
5.7 Vortec / Bravo 2