DIY cleaning procedure for fuel tank follows, but when looking in the gauge sender hole of a steel tank, if its more than slightly rusted on the inside, the tank should be removed, and thoroughly inspected for imminent pinhole leaks on the bottom.... its common for tanks with lots of interior rust to start leaking after a cleaning...
but if it just has some slight surface patches of discoloration, this is normal....
aluminum is harder to tell.... but they usually corrode thru from the outside, rather than the inside like steel tanks.
for cleaning its best if you do this when you only have about a quarter tank of fuel.
get a high volume fuel electric automotive pump and set the intake line (3/8") up with an in-line plastic "see thru" filter.... and pump the fuel out thru the sender hole into a container(s) large enough to hold it all, running the suction line all over the tank bottom, or, if the tank is contoured to the hull, its easy to suck along the lowest edge/corner of the tank.... in pumping this way, you are vacuuming the tank bottom.
you should have a couple extra filters in case you have a lot of debris and it plugs the filter.
then once you have removed all the fuel, reverse the pump and put some back in, trying to pump the fuel up on the sides of the inside of the tank to rinse any particles down to the low point.... than after a gallons worth of rinsing, suck it out again......
at this point, I recommend changing the filter... and then pump all the fuel back in, but DO NOT suck from the bottom of the container, as its possible that there may be some water at the bottom .... keep the suction line off the bottom at least 3 inches until you can see what you are sucking up.... you should be able to put nearly all of it back in the tank... and discard the any water contaminated fuel and the debris laden filters.
with a couple towels and a bit of care this should be a clean job and take about 30 minutes...
but if it just has some slight surface patches of discoloration, this is normal....
aluminum is harder to tell.... but they usually corrode thru from the outside, rather than the inside like steel tanks.
for cleaning its best if you do this when you only have about a quarter tank of fuel.
get a high volume fuel electric automotive pump and set the intake line (3/8") up with an in-line plastic "see thru" filter.... and pump the fuel out thru the sender hole into a container(s) large enough to hold it all, running the suction line all over the tank bottom, or, if the tank is contoured to the hull, its easy to suck along the lowest edge/corner of the tank.... in pumping this way, you are vacuuming the tank bottom.
you should have a couple extra filters in case you have a lot of debris and it plugs the filter.
then once you have removed all the fuel, reverse the pump and put some back in, trying to pump the fuel up on the sides of the inside of the tank to rinse any particles down to the low point.... than after a gallons worth of rinsing, suck it out again......
at this point, I recommend changing the filter... and then pump all the fuel back in, but DO NOT suck from the bottom of the container, as its possible that there may be some water at the bottom .... keep the suction line off the bottom at least 3 inches until you can see what you are sucking up.... you should be able to put nearly all of it back in the tank... and discard the any water contaminated fuel and the debris laden filters.
with a couple towels and a bit of care this should be a clean job and take about 30 minutes...