I have never cleaned out a martin house ,gourd , or plastic gourd and I have had martins for over 30 years, but I do put a teaspoon of sulfur in each gourd ever three to four years this helps keep mites off the birds. I do have some friends that clean out there gourds,
I use some Sevin dust every year.. Sulfur is so very caustic. It burns the piss out of the hatchlings skin if any moisture is present.