¡HÍJOLE!

Rob, I have absolutely no idea about how your drainage system is installed/engineered. But I had a similar problem, i.e., back up overflow thru a sewer pipe, at my store in Red Lodge, MT. Had a device installed at the city sewer outlet point that had a flapper so when sewage/overflow, etc., tried to back up into my plumbing the flappper would close and seal the back up.

We used to call the W.C. in the store "Old Faithful" because everytime there was a back up the toilet spewed a column of water about 3 ft high--the flapper device fixed that.

Would love to be walking the beach in La Barra de Potosi during the tropical rain-a favorite event for me.