low water pressure in tub faucet

would appreciate help. Having problems with very little water coming out of
bathtub faucet. I have already had pressure regulator replaced from the City.
It helped only for awhile, now pressure very low again. The shower in 2nd
bath is O.K. Rest of house is O.K.
I have run a screwdriver up the nipple and a little stuff came out, and after I've done this the bathtub has worked somewhat better but slowly it goes down again. now I have'nt tried blowing any air up the nozzle or anything like that. I figured that would be my next try, I just dread taking the wall down and the tile but if I have to than so be it. Hopefully someone can help me
Thanks: Jack

Is all of the piping galvanized? or just at the faucet? You might be able to remove the galvanized nipple and replace with a brass one, but if the pipes between that el and the faucet are clogged as well, you'd still have the problem. Wait for one of the pros, I wouldn't want my suggestion to be likely to break something...I'm not sure how reliably you can get the existing nipple out. Something is better than nothing.