The sink in my bathroom was replaced by one of those on top of the counter bowl types and now it drains slowly.
I had to lengthen the drain pipe below to get it to the drain coming out of the wall and wonder if the length of pipe is too far from the vent now?
It will drain slowly until enough is in the bowl and then will suddenly all ‘flush’ down. I’m pretty positive there is no clog.
If it’s a venting problem, what do I do to fix?
Here’s a pic.
If it was a problem with the vent it would affect all the drains in the house. I’d guess there’s some sediment in the drain that needs to be cleared. That often happens right after working on the plumbing.
Bowl sinks are the worst idea since the Holocaust.
Who’s been peeing in the sink:o
Thanks for the serious answer. I’ve taken the assembly apart a couple of times and the pipes are completely clear. i’ve also sprayed a garden hose into the wall pipe with zero backflow.
The flushing phenomenon is very consistent. It does it every time you leave the water on.
the drain is a siphon with the trap. the weight of the water behind the trap causes the siphon to flow.
your horizontal pipes after the trap is a down slope from the wall then the siphon has an added load to clear before it flows. this means more water in the sink before it starts. adjust the trap to make this a down slope to the wall.
with the long pipe before the trap this also may be an issue. move the trap higher up and make into a S trap instead of a P trap.
disclaimer: not a plumber
Thanks!
If anything the horizontal pipe has a slight down slope to the wall, It then seems to curve downward inside the wall, but I don’t know what it does after that.
I wonder if there is some sort of test I could do to see if moving the trap up would help, that would be a lot of work to just try out.
Well, I got it working pretty well. Maybe 90% of the speed you would expect the sink to drain.
I replaced the pipes with PVC to make it easier to manipulate and put in a s trap instead of a p. It seemed very sensitive to the height the trap was placed, so I kept experimenting until I think I found the sweet spot.
Isn’t draining supposed to be the no brainer part of plumbing? 
I didn’t realize that anything was a no brainer in plumbing! Shoot, with what they get paid, it must be pretty complicated stuff they’re doing!