go ahead and clean out the tank real good-flushit out. i flush mine with water and then let it dry or use a hair dryer if i am in a hurry.
cleanout the petcock really good also i would a toothbrush and some carb cleaner. and maybe a pipe cleaner to get any hard to reach spots
i do not know your skill level, but with the gas being so filthy i would take off the carb very carefully and remember how things came off. i would then proceed to clean all the components being very careful not to drop anything. once you have the carb back on(check the air filter somewhere along the line) i would check the spark plug.
you can clean it with a little sand paper. if you have the manual it should tell you what the spark plug gap should be. there are tools for adjusting spark plug gap if you do not have one you can get one at an auto store for 3 bucks.
as far as motor oil is concerned just mix the gas and 2 strke oil. your manual should tell you the correct ratio which is usually around 25-30to1
as for repairing that intentionally clogged line in the petcock. i would forget it for now, just concentrate on getting fuel to flow out at a nice steady pace.
as for oil i buy the cheapest 2 stroke oil at wal-mart
really concentrate on that fuel. clean it so it looks brand new.
allso when you flush the tank let water run out the petcock for some tme, but also dump the water out through the filler cap a few times to get any large chunks out.
good luck let me know what happens