hi all, my problem is blue stains showing up in the sink. i rebuilt both toilet tanks, the valves are correct heigth, supply water fills to the line on the inside of the tank every time, and shuts off. i let the lid off the tank, and it looks like once in awhile the water in the tank will rise above the mark in the tank. i dont think the valve has let the water in , so where did it come from? the blue water in the bowl seams to fade to almost clear ( sometimes ). from what i have read on here i am guessing the problem is a bad toilet, or a clog of some kind. the toilet flushes ok , but it doesnt flush the same way every time. i was thinking about installing a check valve in the supply line, just to rule out the siphoning thery. is there any reason that i souldnt install them?? i live in a 2003 doublewide, 2 full baths,. also resently when i let the dish water drain, i hear a gurrgling, i think it is the vent under the sink. how can i test these vents to ensure they are working properly? can anyone help me ?? thanks also the first time i became aware of this problem is water started dripping from my tub ( which i dont use ) and thats when i first seen it. the water does not drip from the faucet. it seems as though there is a pressure change in the supply to it because it only drips once in a while, but for no reason, it hasnt been used?