You don't replace the spout; you replace the entire dispenser. Easy.

I going to replace the entire dispenser but how does it sit on the sink? How does it sit securely on the sink if the spout is too big for the hole that's already there?

This is what the components of a soap dispenser look like - you unscrew the existing one and replace with new. When you do, I’d highly recommend going with something like the NeverMT or similar which lets you pump directly from a full size soap container - so much easier than having to refill the attached bottle with the standard setup. NeverMT on Amazon: https://amzn.to/3AubMYw

If you decide to install the NeverMT, learn from my mistake and look under the sink occasionally to make sure it is working properly. Mine failed, and I ended up with a quart of liquid soap that oozed out of the tube, down the soap container and onto the cabinet base. What a mess to clean up!

And in case you didn't know, you can fill the small bottle (pictured above) from the top of the sink using a small funnel. You don't have to unscrew the the bottle from under to refill.

Love my NeverMT. One of the best additions to the renovated kitchen. Thankfully I bought another one because we are moving into our last home and renovating that kitchen!

As far as checking on the detergent container for leaks I actually used a long plastic under the bed storage container under my sink in case of leaks from any cleaning products stored there.