Chickenpants,
The woman contacted LE on Monday night.Very early on in the investigation. She was highly specific about them needing to search the Gano House.And,even more telling, she said they should check that dumpster too.
I will *speculate* that she told LE why she felt they should look there. It could be that it was a hang out place for kids,including Somer. Most likely they might hang there after the construction workers had left for the day. If you think about it , she would have told them to check the dumpster BEFORE LE came up with the plan to follow the garbage trucks. I have never heard of a LE agency following garbage trucks before during a kidnapping or disappearance.
About the dogs : she might have been moved from the Gano dumpster,and placed in another dumpster. Especially if she was in a heavy duty plastic bag,and moved in a car. I have heard that scenthounds are not always able to get a scent on a person to find them.
Guessing that she ( the tipster) was scared,and wanted to remain unidentified.
Or she had some part in it. This is a multi killer not just one in my opinion.