in that case, I again would be draining system as much as possible, new filter/'s and run just a bit and repeat 2or 3 times!
the filters might be rather important too, as I'd gather fuel will work like a cleaning agent, and possible loosen up crud that has been struck for a while, and will now freely be moving about!
I used to see this a lot in ATV, that got sunk, and then owners flushed the systems with diesel fuel or kerosene to try and remove water and dirt that went in with the water, the diesel fuel/kero, maybe cleaned things, some, but it also again loosened up old grim that was safe/safer as it was ) so replacing filters is a good thing, minus there costs!
as I doubt having gasoline in your pump and how it may effect seals is going to be a good thing,
and there is no really good way to drain system 100% , you always end up with some fluid in hoses and places gravity doesn't fully get it out!
so, its going to take a few fill, run a bit, and drain again, to flush the system clean or clean enough IMO!
sucks, for sure
but as in life we all some times learn things at a cost!
Maybe others here will have better suggestions, but that would be mine!
best of luck to you
and I would want to get this done ASAP, and not give the gasoline time to dissolve or eat on seals and gaskets!