05-01-2019, 09:46 PM
I have seen semi-slugs crawling across the shade cloth cover on my 10,000 gallon corrugated steel tank at least a couple of times. The risk is definitely there that the slugs will find a way into the tank. I had taken the cap off of my first flush device at one point and was just running on what was in the tank so there was access there and no water in the overflow. After a few weeks I discovered slug trails inside the piping that had always been clean before. That horrified me. I disassembled what I could and cleaned the dickens out of everything, then plugged the system inside the tank and filled it from the roof down with a heavy clorox solution for a few hours, then put a quart into the tank through the piping so it would create a zone of death in the bottom of the tank. I had not read this report yet but I already suspected that the larvae and certainly the slugs would sink. At that point I put screen over the outlet of the overflow. Pretty stupid that I hadn't already done so. At this point there are only 4 points where the shade cloth has small gaps where pieces overlap on the tank that the slugs could get in to the tank directly. If they entered through the gutter system they would have to make it past the first flush device which is not likely.