slow and fast bathroom sink drain

[carguy148]

Hey guys my first post. I hate to come right off the bat with a qyuestion but, here goes. The sink in my first floor bathroom tends to be slow, I usually get it working better sometimes but usually on the slow side. So I just did the baking soda/vinegar trick followed by really hot water then the tap hot water. Well for the first time since I've lived here I had that thing flowing, no water buildup in the basin and just chuggin away. Well after admiring it for a few and not wanting it to ever stop I turned off the water and I hear a gulping noise for like a minute. Well after that I decide to test it again, back to it's usual slow self. So I mange to do it all again and yep got her working then turned off the water and gurgle gurfle gulp. Why? iI there some valve along the way that could be floating back into a stuck position. Like I said it's better than it was when I started but man that thing was really sucking for a minute there, twice. Any help would be greatly appreciated.....

[HayZee518]

downstream of the drain is a trap. it is shaped like a P or an S. Some have cleanouts, most don't. its function is to keep sewer gases from emanating through the drain opening. standing water and effluent bodily fluids build up bacteria which changes the water to a gunk like consistency. this slime needs to be flushed out so it doesn't adhere to the walls of the pipe. use a chemical drain cleaner like DRAINO. the crystals is lye and Magnesium flakes. The action creates heat which is supposed to dissolve the gunk.. Flush it with cold water when you are done.

[carguy148]

But why is it if I put a tee kettle of hot water down the drain and turn on the faucet it will all run thru and then keep running thru till I shut off the water? And when the faucet is shut off and all the water goes thrue there is then a gurgling belching noise going on and when that ends I turn on the faucet and it fills the pipe then the basin starts to fill then when I turn the faucet off it drains just rather slowly. My logical mind is telling me that if I can get it too flow completely at one point then there must be no blockage. I don't know if you could explain why it would flow after putting a kettle of boiling water down makes it flow then i hear the gurgling maybe it would make more sense..... Thanks in advance once again.....

[HayZee518]

another thing to check is the distance from the vent to the drain. a drain runs because of make up air travelling with the water. a partially blocked vent due to a bird's nest or something will cause problems.