Draining the tank is pretty easy.
Just pull the supply hose off the fuel pump, & the syphon effect will drain most of your tank through there.
Then jack up one side of the back of the car. Remove the pickup/ sender fitting from the tank. Be gentle, the rheostat in the gauge sender doesn't like rough treatment.
Insert a hose through the hole, & across to the now low side front of the tank, & suck to start the syphon, into a bucket. Go have a beer to get rid of the taste of petrol. Come back & be horrified at what came out of your tank.
I found I had to add more fuel, & repeat this syphoning process twice more, before I stopped getting silt & water, as it is hard to get the last bit.
Not too long after this, [a year perhaps] my tank rusted through from the inside, so if your tank is original, replacement may be the best idea.
Hasbeen