The rhetorical question that begins with the words "Who can pour out" in verse 37 ends here. "Only I can pour out ... when the dust runs ... tightly together." (See: [[rc://en/ta/man/translate/figs-rquestion]])
The rain makes the loose dry dirt stick together like one piece of dirt. This can be stated in active form. Alternate translation: "when the rain molds the dirt into a hard mass" (See: [[rc://en/ta/man/translate/figs-activepassive]])