How do you get the drain out of the tub so you can run a snake down the drain to clear the drain?

Most likely water pressure switch needs replacing.

Few plumbing issues such as Dripping faucets. Running toilets. Leaky valves. Clogged bathtubs can be solved by our own trying few things.
1)Firstly lookout for what is causing blockage such as soap or hair inside the pipeline blocking water just pull it out from pipes.
2)Secondly use a plunger(Tool used by plumber to clear clog) pour some water in bathtub to cover the plunger block the overflow of water with rag.Place the plunger over drain pull up & down 5 to 6 times.
3)Lastly if still the clog is not cleared try out with snake a long flexible steel cable wound on a handle In a sink you just feed the snake down the drain, but on a bathtub you need to feed the snake down through the overflow plate opening. Start by feeding about 3 feet of the snake into the opening, turning it as you push it forward. You will feel some resistance as you work the snake through the trap under the drain, and the turning helps to move the head through the trap. The snake should either break up the clog by pushing its way through it, or your turning will hook the end of the snake onto the clog and you can pull it out.

After trying with above if still there is plumbing issue call sewer line repair services for help.






Grease Trap Services

use a snake
http://www.wikihow.com/Snake-a-Drain

Assuming you have a lever operated tub stopper, with the lever mounted in the overflow plate, a common malady is the decay of the internal end of the lever, leaving the stopper at the bottom of its pathway preventing drainage.

remove the overflow plate and carefully slide the stopper assembly out of the overflow... you will know almost immediately if the assembly has come apart. if its intact, run a small diameter sewer snake down the open overflow to clear the tub's drain trap. if it has indeed come apart, remove the connecting rod and stopper from the overflow, you may have to fish for it some. Happy hunting....

reassembly is simply reversing the removal process once you have replaced any broken parts or cleared the trap.

if no drain at bottom usually with hose connection on it use a sump pump or syphon make sure power is off until fully refilled

go to hardware store like lowes or homedepo and go to plumbing isle and look for a plumbing snake get the small one witch usaly 20 to 25 ft long its real easy to use,all you do is put end of snake in tub and start cranking or turning handle alloying snake to go down pipes it will turn around in circles freely until it hits clog then you pull and push it into clogged pipe until it cleares out

you have a blockage in your drain line. you could snake it, pour drain cleaner in or do both. once your unblock it the smell will clear up.

Something was flushed that should not have been flushed
You will have to have your drain snaked out.

I take it that you removed the drain trip linkage and stopper through the vent hole .
You must now run a small hand or small power snake the less than eight feet to open the drain.
You can also plug up the vent,tightly and  try a flat plunger on the tub drain .