bathroom sink draining slow

Hi all,
My bathroom sink is draining very slow. I took off the trap and the connecting pipe all the way to the wall and cleaned them out really good. This improved the situation, but did not correct it. If the water is not on all the way it can handle a small stream without backing up. I did a little test and the stream it could handle took 15 sec to fill 16oz, take that out and that is 0.5 gpm. Anything faster and it fills up and drains really slow. I tried to snake the drain line but was unsuccessful. It 45's right out of the wall and I don't know what it does after it is in the wall, but I could not get it to go much past the 45. I dont know if that is b/c there is a clog there or I just dont know what I am doing with the snake. The pipe is galvanized and it is a 50 yr old house.

Does this sound like a venting issue? Should I go back at it with the snake?

The tub in this bath drains kind of slow top but does back up like the sink. I have not atempted anything with the tub yet. I just didnt know if that info would help.

Thanks so much for any and all feedback.

This may seem obvious, but have you checked the top end....i.e. the pop up stopper itself and the area around there. This is ofter where a lav stops up.

thanks for the reply jimbo, but yes that is clean. You can actually see the drain fill up as the water rate increases. That is why I dont know if it is a clog or venting issue

From what you say, I would buy an inexpensive top snake in a can.

Take the stopper out and leave the drain connected . Slowly turn right and then left an and push the snake into the sink until you are into the vent pipe.

Shouldn't be more than 8 feet to the vent. Run a little water at the same time.

thanks,
I do have a snake and tried going directly into the wall thru the galvanized 45 and got nowhere. Is it easier to get there by going thru the sink? Would it be worthwhile to get up on the roof and snake the vent from above? thanks again.

My preference is to go through Through sink with water flowing, or flowing intermittently at least. Otherwise I would use a small motor driven snake.