A:  Yes, the Mosquito Dunks are actually labeled for use in animal watering troughs. There will be no issues with your dogs drinking the water.

A:  Yes, this is absolutely safe for pets and wildlife if they drink the water the mosquito dunk is in. 

A:  Using only one should be sufficient. Read the instructions for clarity.

A:  I put 1 and when it dissolves another. Mine has a lid with screen opening.

A:  Each Mosquito Dunk covers up to 100 square feet of surface water regardless of the depth. For a 55 gallon barrel, 1/4 of one Dunk would be sufficient.

A:  Because mosquito larva are only in the top 1 inch of water, and due to the circumference of a 55 gallon barrel, you only need 1/2 of a mosquito dunk ring once a week.

A:  If you gutters hold water, you should have them checked.  any standing water can be treated with these tablets

A:  The dunk must be on top of the water.  If you could secure the dunk, so that remains on top of the water, it most likely work.  I am not sure why you would have standing water in gutters, unless the gutters have not been cleared of debris.  Water should leave the gutters very quickly, if the gutters are clean.  We have used these dunks for at least 7 years & probably closer to 10 years.  they do work very well, if the directions are followed.  We have several 55 gallon barrels for water collection.  Each has a screen wire covering & I place a dunk on each cover on the areas where water pools.  We have no mosquito larvae!  

A:  Yes, perfect for use in gutters. Tie a string through a hole in the center of the Dunk and secure it to the gutter so it does not wash away.

A:  Gutters should not be a source of standing water. Gutters should be catching the water as it comes off the roof diverting it to a downspout and then dispersing it away from the structure, However, if your gutters are clogged and you have standing water in them, then putting mosquito dunk in there will work to kill any mosquito larvae. 

A:  Sorry, not for no see um larva.

A:  As far as I could tell, yes but we go through rain water fairly quickly. But at times we do let it sit and baby biters form. The dunks work. 

A:  There is a possibility it may as Mosquito dunks consist of a certain type of bacteria as their main ingredient: BTI. Bacillus thuringiensis subspecies israelensis (BTI) is a type of bacteria that kills mosquito larvae before they hatch. This BTI also targets the larvae of fungus gnats, black flies and biting midges (no see ums). 

A:  I think so. I know that I have no problems when I put these down. They last a long time as well.