I have a clogged sink and I used a snake with a drophead.It goes up to the air vent instead of through the clogged pipe. I also tried flushing the clog with a garden hose and water. Water flushes through but remains clogged when there is no water pressure forcing it. How do I get the drophead snake to go through the clogged pipe instead of the air vent on the roof?

If its only a sink that is clogged the junk is not in a main drain so its unlikely rodding from the roof will reach it. Remove the trap and rod straight into the wall with a rotary snake on an electric drill

Thanks ballengerb 1 but I don't think I explained the problem clearly. I did remove the trap and was rodding through the wall. There is a T (if that is what it's called)
Where the pipes meet.The snake would take the path of least resistance and go up and through the air vent to the roof and dangle on the side of the house.
After 4 attempts and proceeding slowly it finally went the right direction and unclogged the junk. Phew!

That TEE should no have been a TEE for the exact reason you describe. Iy should have been a Wye Fitting Slip x Slip x Slip, Buy PVC Pipe Fittings Schedule 40 Online

Hi guys...

Actually Bob, I have a different take on that.. ;) A sanitary tee fitting is the appropriate fitting in this case as it allows the vent to act with the centerline of the drain (ptrap). If a wye or wye combination fitting was used, it reduces the vent contribution at the PTRAP... something inspectors in most places won't allow (see image).

As much as it sucks when snaking the drain it is what it is! In my area, we actually install a cleanout tee in washing machine vents for this reason :)

As plumbinjack finally realized, if you go in enough times with a drophead on your snake it will eventually drop and go DOWN the drain! Glad you're all set, Jack!

Mark