If you can, pump out the fuel, clean up the tank with rags etc. on a stick. Then filter the fuel back in after settling - or if dubious, throw it away.
If you can get a pipe to the bottom of the tanks you can pump out the bottom fuel until it looks good. This is a less certain method but worth trying if you cant get at the tank interior.
NB - Its amazing what you can find in a tank. I've had something big enough to block an 8mm. dia pipe. - and orange hair!!
On this subject would be interested in other's views.
Because of increasingly dirty fuel filters I opened up the buit-in fuel tank on our steel boat. The tank is part of the boat's construction and is in the top half of the keel - accessible by three covers. Having sucked all fuel out and cleaned out all the sludge etc I noticed that the fuel uptake pipe was long enough for its opening to be virtually touching the bottom of the tank - thereby ensuring that any debris would be sucked up. I thought this was ridiculous and discussed it with the chandlers (we were in Horta at the time and the chandlers there are very experienced) who agreed with me that I should cut off a bit of pipe so that there was more chance of clean fuel being sucked up. So I cut off a bit over an inch of pipe and refitted the covers and filled up with fresh diesel.
I was discussing this a day or two later with a very experience delivery skipper and proudly saying what I had done. He said that although he understood my thinking I had done absolutely the wrong thing. In his view the installation had been correct. If you don't have the pipe taking fuel from the very bottom of the tank he said, you create an environment at the bottom for the collection of water and debris and bacteria growth. Much better to take from the bottom and let the filters do their job.
This makes good sense to me and I wonder what others think. I haven't remedied the situation yet though!
If you don't keep the fuel cycled and clean (that's what the filters are for) then all that gunk on the bottom is going to just build up worse and worse. Some of it is from dirty fuel, but as that delivery skipper explained, some of it is from water and algae growth.
Then comes the day that the weather is really bad, you're tossing and turning and rolling around and trying to motor out of the slop when the engine quits because all that gunk in the bottom of the tank has been stirred up so badly that your filters are clogged. And things go from bad to worse. You change the filters in the terrible rolling, sloppy conditions, and because there was so much gunk the fuel is hopelessly dirty and these filters clog up as well! Now what? Do you have a third set of filters aboard? Yikes!
do you have an agglomerator in the fuel line before the primary filter? it should collect all water and the debris dissolved in it. you can periodically open the valve at the bottom and drain off the grot. using this setup i've only had to change the primary filter once in over 1000 hours of motoring.
ta guys for your advice.
is the "agglometer" thingy a plastic bowl with a transparent bottom ?
sorry to sound so ummmphh but still learning.
this bowl is before the primary filter and i can see crap in the bottom. it does appear to have some type of drain.
Reading between the lines, I wonder whether your question is related to your newly-acquired boat? Did you have a problem with fuel during the delivery trip? If so, this is very common indeed. Many boats sit unused for long periods prior to being sold, and new owners often have to deal with fuel contamination problems.
It might be worthwhile considering getting your tanks professionally fuel-polished. This should remove the majority of the rubbish rather than letting your filter deal with it. There was a MB&Y article a while back about Expresslube, who offer a mobile fuel polishing service. I've no idea whether they're any good, but the process isn't exactly rocket science so it's really more a case of finding someone with the right portable kit. Could be worth a look.
an agglomerator is a vessel, sometimes with a glass bowl at the bottom, which collects the water and crud at the bottom. the fuel flows in over the top of a cone and the engine feed is from underneath the cone so anything heavy has a chance to settle out. a tap or plug at the bottom allows you to drain off the crud.
because inland waterway regulations forbid the glass bowls and valves, new ones, even on offshore boats, have all-metal bodies and plugs requiring a spanner.