wherever your water is running slowly, tub sink, you can use a shop vac to clear any obstructions causing the slow drain, usually in the kitchen, not using a strainer and allowing food and dumping grease will clog a drain pretty fast, in the bathroom tub or shower, hair is usually always the culprit. at any rate, a shop vac works like a charm on anything stopping up a drain. just take out the filter and make sure you seal the hose over the drain with a rag so there's no air coming into the hose, creating a tight seal will cause the suction of the vaccuum to work on anything in the pipes. you will want to run water first to back up the drain, the cohesion of the water will clear the pipes. you'll be amazed at what comes out. using a snake will only loosen the material and not clear it out completely and running water after that will only make it clog further down the line.