Bathroom sink drains slowly. I have dumped chemicals, used a plunger, tried blowing out with scuba tank air hose and it still drains slowly. I brought the garden hose in and turned it on full after sticking down the drain and blocking off any leaks. The water (lots) goes through the pipe OK under hose pressure but then drains really slow once there is no pressure. I thought of trying to snake but I am afraid that the snake will go through what is blocking just like the water did under hose pressure. Any ideas?

I thought of trying to snake but I am afraid that the snake will go through what is blocking just like the water did under hose pressure. Any ideas? Think again! The only way you're going to clear that drain is to run a snake through the trap tai,(see image) up into the wall. You will run into a bend about 6" in but work your way around that and you only have to put out 5' more. After you put the trap back pour a couple of large pans of boiling water down the drain to looosen the grease and flush the mess away.
Good luck, Tom

So I tried one more thing before I filled the drain pipe with gunpowder... I did run a snake - twice and worked it in and out as best I could. Nasty, nasty... I then connected the garden hose to the bottom drain of the hot water heater and stuffed the other end in in the drain with some rags to keep it form leaking. Had the wife on a walkie talkie and said let her rip... Don't know which of the above did it but the drain flows freely now. All is good.

Glad it worked but that's a pretty chancy way of doing things. Most heaters are around 120-130 and can do a bit of damage to you if you let loose of the hose. Glad you are back in business.