I know that hot water can soften PVC drain pipes causing them to sag in the middle of long unsupported runs. Maybe a pipe starts sagging causing an uphill climb on the downstream end? Seems like it would take a lot of hot water to soften the pipe that much though... Or maybe the hot water is softening something in the sink drain-stopper causing it to sag and block the drain... ? I am not a plumber :)

Well, the pipes won't sag when you use hot water and then go back to normal when you use cold water again next time. So I doubt that that's the issue. Maybe try lukewarm water and see if that makes a difference also, that would suggest that something does soften above a certain temperature.

I also had similar problems with my wife's hair, have a look at the drain traps on the link below, still haven't purchased one but I wonder if they do what they promise.

Here is a link that might be useful: Non-clogging drain traps

The only explanation I can think of is that the hot water is softening up the residual goo (technical term) that's lining the pipe. Maybe filling the bowl with hot water + detergent will release more goo and wash it down the drain.

i am having the same problem with my new sink! it has only been 2 days since a complete new sink has been installed in my new bathroom. so definitely the pipes are not clogged.Has anyone been able to resolve this issue??
However, i tried the solution posted by homebound and everytime i pour detergent in the still hot water sitting in the sink, the water instantly drains out. but if i open the Hot Water again...the same thing, it won't drain. what to do?? please advise. any suggestions will be appreciated. thanks.

Hot water warms the air, and warm air rises, lowering air pressure at the surface. That's weather. You have a microclimate. Rising moisture and warmer air create a column of low pressure above the sink. It must be creating enough uplift to counteract the usual effects of gravity and atmospheric pressure. With cold water and typical high pressure, I would expect water to flow down through plumbing faster. This might just be an extreme case. A partially clogged drain or vent wouldn't help.

Shipshape I don't know if you're right but that is one great answer!

It is getting harder to find a new sink with an overflow... wish it was a requirement.

On every site I read about this issue on, "hot water drains slower than cold", the common answer was "It's impossible". Well I'm here to say... "Whatever!"

My kitchen sink was doing the exact same thing (thus, my Googling for a solution); cold drained normally... hot backed up and started to fill the sink. Tried Drano kitchen crystals; boiling water (it just filled up and sat in the basin); plunging it (made more of a mess than anything); checked the trap; tried baking soda and vinegar, a Coke, etc. All limited, if any, improvement.

What finally worked? Leaving the hot water running (until it finally ran cold on it's own, so an entire heater tank's worth), starting out slowly (thus, a constant flow) and lightly drizzling Dawn dish detergent down the drain with the hot water flow. It still filled up, but slowly started to drain, then started to bubble and burp, then started to flow, then the drain rate finally started keeping up with the flow, at which point I used my sink sprayer for a little more pressure, all the while periodically just lightly drizzling Dawn right down the drain. I can only assume there must have been some sort of fat/grease clog, and over the half hour or so of actually FLOWING hot water (once I got it started) and $1 mini bottle of grease-cutting Dawn over whatever the clog was must have broken up and washed down enough of it so it finally drained normally regardless of water temp. As such, I'm guessing the above theory was accurate and the hot water vs. cold was just heating up the clog, causing it to swell or whatever, thus decreasing the flow of JUST the hot water.

Anyway - it's worth a shot to anyone experiencing this. And don't let any "backyard physicists" tell you it's "impossible". ;) LOL

I have the same issue with my Vessel sink (without an overflow drain). The problem I have is when the water gets super hot it starts to slow drain, filling the sink up about half way. Then all of a sudden it will start to go back down and fully drain while the hot water is still running. Doesn't do that with warm or cold water. I have all new drain pipes (to wall), also the problem actually started after I replaced my Water Heater (getting much hotter water now).

I was thinking it had something to do with the expansion of the metal drain in the hot water. I liked Ben's answer of surface tension in the small holes of the drain. Then maybe the weight/force of the water in the bowl breaks that tension and it drains. I tried the straw test and it worked (kind of acts like a breather valve). Maybe there is a drain with bigger holes or I will drill one or two holes larger.

I have the complete opposite problem. Hot water drains fine, cold doesn't