Why you should not leave your grey valve open - Sewer Rats

Speaking of the sewer flies....I kept finding the occasional black sewer fly in my shower. I never leave the gates open, so I figured it was just a random fly. Then one day I saw something wiggling near the lower track for the shower. Turns out it was a sewer fly maggot, one of many, that was living in the moisture under the track. Thus, the occasional fly on the shower wall. Once all the maggots were destroyed, no more flies.