Plumbing – Sink basin gasket leaking

It should not be necessary to try to goop some type of sealer around the lower neck of the sink drain. Such solution may work but it is not the desirable approach when you consider that someday this assembly will need to come apart for repairs.

In looking at the assembly that you have I wonder if one or more things are at play here.

1) If the drain pipe tail was not centered in the neck of the sink drain and then had lateral force on it due to the down stream goose neck trap it could be forcing the gasket open on one side. Check that there is no undue large amount of sideways pressure on the lower part of this pipe assembly.

2) It looks like the gasket directly contacts with the face of the capture nut around the drain pipe. It is possible that by tightening the capture nut that it is putting a twisting force on the gasket that may cause it to "fold away" from the sealing edge of the sink neck.

3) It is possible that there could be a small crack or pitted area on the sink neck that keeps the rubber gasket from engaging 100% with the sink neck.

4) Sometimes the "rubber" used in this type gasket is made of a plastic material that is anything but rubber. Check at the local hardware store to see if they have another gasket that is more pliable. In some cases a silicon material may be better.

Remove everything currently under the sink that is not glued and use a rags to plug the drain pipes. Next, let the counter guys do there work and install the sink. There is nothing to do until they are done.

After they are done, follow the install instructions on the disposal. After that is done, mount a new p-trap kit from one of the drain pipes to the disposal outlet. Choose which one works best. The other drain pipe you will need to cap. Since this is under a sink, you can use a compression based cap so if in the future you decide to go back to a two sink setup it will be an easy job to removing the cap.

There is no harm in trying and if you find it doesn't work/leak just call a plumber. The plumber I use, this would just be a service call charge ($45) to install.

Also if you plan to reuse your current disposal, remove it and the mounting ring before the counter guys come. I had a friend who had they counter/sink redone and the counter guys left with the disposal mounting ring still attached to the old sink. They had to buy new hardware to mount their old disposal.