I only use a 1 gallon pitcher to transfer the water. My HLT, (round cooler) is lower than my mash tun. I do float a lid off of a 5 gallon bucket on top of the mash and the lid floats fine. I just pour the water in 1 gallon at a time on the bucket lid. Also, I usually keep the mash tun FULL...
Do you use a garden hose to fill your brew kettle? If so, I would bet those things came from inside the hose. Especially if the hose is left outside with water in it.
Just a thought because I have seen similar strings from my hose when I fill the kettle. I usually let the water run for a...