This very effective tip is still not wellknown and we must share it.
Here is the best way to unclog a sink or a toilet.
1) Place the garden hose in the pipe.
2) Let the water flow.
3) The toilet or the sink should be unclogged instantly. If it's not the case, make a back and forth motion with the hose into the pipe. And think about blocking the overflow with a wet rag.