This is a problem I have seen...
When I bought my X Sport, it had sat for a number of years...I thought I cleaned out the varnish and old fuel and put in a new used pump...The first indication I had a problem was when the engine wouldn't pull past 3k rpm...I pulled the fuel filter and the rust and brown fuel that came out the inlet side was awful...
I replaced the filter and had to replace it every 3000 miles or the engine would start dropping fuel pressure...I installed an electric fuel pressure gauge to monitor the fuel system pressure especially when I would accelerate quickly and I could see the drop in pressure as the filter got plugged from the tank...
After the new used pump seem to be dropping pressure after 30-45 mins of running I installed a new pump in August...I was still getting a dirty fuel buildup on the inlet side of the filter but figured that it was from an unknown gas station...Little did I realize that the tank was causing this problem all along...
My new pump died earlier this month suddenly and I decided to fix this problem once and for all... The strainer on the bottom of the pump is a large particulate filter that lets dirt, rust, and other smaller garbage flow through just fine...The brown crap in my fuel is coming from varnish buildup in the tank that the sloshing of gasoline disolves as you drive and fill the tank...
So I drop the tank and have a radiator shop boil it out...They drained over a gallon of dirt, varnish, and rust out on the first pass...And then they started dropping into the big tank and it was ready the next day....
A new pump, a clean tank, and 200 miles later the new filters inlet is as clear as the 15 gallons of fuel I poured back into the tank after pumping it out before dropping the tank...