Re: possible gas leak in belly tank
If it's leaking that bad you have a serious safety issue--hope the bilge pump doesn't click on! followed by a serious enviromental issue.
If the boat isn't on the trailer get it on one; flood the bilge before operating.
Drain the bilge but catch the oily water; do not let it go into the ground or worse down the ramp.
Disconnect the battery while you are flooding the bilge (assuming the batteries are nearby)
Get a professional company to pump out your tank ASAP. We have companies here that come to your boat to do it.
Now, if you are exagerating about the "sump full of gasoline" and you have a little gas in the bilge water, do the same as above but it's not quite as serious. Yet.
Any way to determine if you have a bottom leak, or a top leak around the fills, sending unit, etc? Or where a hull component has chafed through? leaky hose or vent?