I would drop the tank if the old gas is in question and there is a question on debris inside.
Is the gas that is in there smell bad? hard to suck out the old gas from these things. How about sucking the old gas out and putting in some fresh stuff and re-sucking?
Dropping the tank is a bit of a pain but doable, have a friend help in holding it while you unbolt it. Just make sure you are very careful when your disconecting the plastic clips that holds the hoses on the tank since they are old and will probably be brittle.
Pull the pump and it will be easy to see inside and clean, which will lead to the next question, how old is your fuel pump? If i was going to pull the tank and pump, I would spend the money and put in a new one since you will probably need a new gasket for the pump assembly. Yea pumps assembly is expensive but do you want to do it over again if the pump fails next week?
My truck was recently involved in a accident and the bed had to be removed, so I replaced the pump from the top since it was exposed, pump had 70k miles on it,over kill ? maybe, but I just considered it part of my maintenance so that I wouldn't have to drop the tank.
The guys who invented in tank fuel pumps should be shot!