Very perplexing problem! So here are the only thinks I can think of.
When you pulled the garbage disposal, did you remove the black disposal elbow from the disposal? If not, check that connection. There possibly could be something like chicken skin, like MrInfoPhilly said, that is acting like a flapper valve when it is installed in the exact position in the sink.
And as this just started, I doubt this is the problem, but mark the position of the black disposal elbow where it goes into the P-trap and assemble it with the P-trap out from under the sink. Those disposal elbows are to be cut to size, and perhaps it is sticking down too far into the P-trap restricting flow. Even if it is, it shouldn't cause an immediate backup that takes minutes or hours to drain, but perhaps something funny is going on with that assembly.
And as TomFOhio asked, can you see into the wall if there is an elbow or a tee. The issue he is asking about is probably a venting issue. Again, I can't believe a clogged vent on this drain would cause this issue, but perhaps that is a possibility. Water from a hose under pressure with an air gar around the hose is a lot different than a gravity drain hard piped to the drain line. I would agree with you that the water flowing easily down the drain with a hose with no issues would rule out a clog more than 25 feet, so that would be my last step after verifying every other possibility.
Good luck.
When you pulled the garbage disposal, did you remove the black disposal elbow from the disposal? If not, check that connection. There possibly could be something like chicken skin, like MrInfoPhilly said, that is acting like a flapper valve when it is installed in the exact position in the sink.
And as this just started, I doubt this is the problem, but mark the position of the black disposal elbow where it goes into the P-trap and assemble it with the P-trap out from under the sink. Those disposal elbows are to be cut to size, and perhaps it is sticking down too far into the P-trap restricting flow. Even if it is, it shouldn't cause an immediate backup that takes minutes or hours to drain, but perhaps something funny is going on with that assembly.
And as TomFOhio asked, can you see into the wall if there is an elbow or a tee. The issue he is asking about is probably a venting issue. Again, I can't believe a clogged vent on this drain would cause this issue, but perhaps that is a possibility. Water from a hose under pressure with an air gar around the hose is a lot different than a gravity drain hard piped to the drain line. I would agree with you that the water flowing easily down the drain with a hose with no issues would rule out a clog more than 25 feet, so that would be my last step after verifying every other possibility.
Good luck.
