right, you need to address the rust in your tank. magnets are ok, but they are not a solution. theyre ok to prevent probs in a treated tank, but if you can see/hear rust in the tank, then you need to address this problem NOW! i guarantee that if its going to fail and leak, it will do it xmas eve, new years day, or half an hour before you set off on an important trip. you know the score. ok, if you cant source another tank, then get your tank off, drain the fuel, and get the loose rust swilled out. (boiling water and fairy liquid is a start, but do it outside and dont smoke when you do it) after you have drained the crap( amagnet on a piece of bamboo swirled inside picks the big bits out ok) you need to dislodge the rust in there. some folk say a handful of gravel or nuts and bolts shaken round inside the tank, i use a length of chain with nuts and bolts through the links and shaken vigorously, works the same as the others, but is easy to get out afterwards. once the loose stuff is out, you need to try and remove as much as possible that hasnt been knocked off by the shaking. im not going to go into details, but try googling 'electrolytic rust removal' you need an old type battery charger but it will remove most rust from inside tanks. leave it like this till its clear, and then get a fuel tank sealant. you need to make sure that the sealant can cope with e10 petrol, the ethanol in modern fuel can dissolve fuel tank liners if they arent made to cope with it.
i know this is a faff, but until you sort out the problem in your fuel tank you will never be free of fuel and carb problems, cleaning the carb and the magnets will only put off having to do this for a few weeks at best. but a few days should permanently sort this.