How do I fix a sink that became slow to drain after pouring polyurethane down it?

Question

Situation and problem

My buddy has a woodworking shop which he graciously allowed me to use for a woodworking project. I am a total novice in these kinds of areas, which will be doubly clear in a moment.

After applying the last coat of polyurethane to the project, I had about 2 tablespoons of polyurethane left over in my cup I was pouring out of.

Being very unwise and uneducated, I poured about 2 tablespoons of polyurethane down the shop sink. (For those on metric, Google tells me 2 tablespoons is roughly 30 milliliters.)

Now the sink drains very slowly. I'm assuming this is because the poly solidified in the pipes and created a partially obstructed drain. That's just my newbie guess, maybe some different interaction happened.

Additional details

I did an internet search before the cleanup stage to see what dissolves polyurethane. So I mixed the poly with some paint thinner before pouring it down the sink. (Later, I learned neither poly nor paint thinner should be poured down a sink.) In any case, it didn't seem to make a difference related to the blockage, as the sink still ended up draining very slow.

My buddy knows about all this. I'm just trying to get additional info so I can get this fixed for him and correct my mistake.

My buddy says that the water from his shop doesn't go directly to a city waistline. It goes to a sewage ejector pump that's in the shed outside. And this sewage ejector pump doesn't operate all the time.

One thing I've researched, but haven't tried yet, is using vinegar to dissolve any polyurethane blockage. It's safe to pour down drains, and supposedly vinegar dissolves poly. Though it might take a large volume or be a very slow unblocking process?

Help appreciated!

Any insight into how I should proceed would be much, much appreciated. I certainly don't want to make things worse as I try to make them better.

Answer 1

Start with (no, wait - buying your buddy a large quantity of the GOOD version [in your buddy's opinion] of something they like a lot, then...) removing the trap, assuming the trap is not one that has to be sawn out to be removed (I hate those, and I hate the people that put those in anywhere but underneath a concrete slab.) A nice normal trap is unscrew 2-3 slip joints with a bucket to catch the slop and get right to the guts.

At that point you may well find your major blockage, and be able to either remove it, or simply replace the whole trap if it's stuck to the trap very badly. If you need to snake, better to start with the trap removed if possible, it takes one set of turns out of the start of the run.

Alternatively, just call in a plumber...