Clogged Tubs and "The Ram"tm (Compressed Air)

My building maintenance guy can't quite communicate with me, or doesn't want to. Every time I ask them to come up and clean the stoppage in my bathtub, they charge $30. He uses an industrial-type device that works like this... you crank it (like an old water well) building up the air pressure. When you have enough pressure, you put the nozzle end over the drain hole and press a trigger, which releases all the compressed air into the hole. This never fails to unclog my tub drain (the only one that clogs here).
Does anybody know the exact name of this device and where I can buy it? I know it is going to be over $100, but I don't mind.
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They used to sell compress air in a can that was just for this. There are also bladders that fit into the pipe and use water pressure. You might need an adptor for the sink faucet to use one of these. Buy a strainer for the drain. Use Ammonia 1/2 quart every week then run 20 gallons of hot water. The ammonia should clean out the sludge left in the pipe from years of draining away the oils and hair.
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Use the money to buy a wet/dry shop-vac, and clean the drain with that.
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