http://lawnandgarden.manualsonline.com/manuals/mfg/weed_eater/545117526.html?idRes=15826863
This link should let you obtain the manual for detailed instructions with photos.
If this is in fact an Echo SRM 210, then a manual is linked below.
Nylon
A line trimmer, also known as a string trimmer, is used to trim grass or weeds. The piece of equipment also goes by the name of a weed eater, or weed whacker.
Locate the trimmer head at the shaft. Remove debris in the head. Cut a 14-inch piece of the trimmer line and fold it. Place the spool against the spindle. Feed the ends of the line through the eyelets. Push the spool down and pull the trimmer line tight with your hands. Tighten the spool.
It is easy to string a dual line Remington trimmer by following the instructions in the manual. The manual was supplied with the trimmer when purchased.
This is actually easier than it first appears. # Line up the two arrows on the outer-spool and inner-reel. # ## This opens the channels from the feed-holes to the locking holes. # Remove any line left in the locking holes. # Feed new line into feed holes up though the channels until you have enough to place the ends of the lines into the locking holes. # Place line ends into the locking holes and pull tight. # Wind the inner-reel counter-clockwise, taking up the new line. Pause occasionally to pull each line tight. Leave about 4 inches at each end.
You can expect to pay about $5 for replacement line for a Poulan Pro trimmer.
Yes it can, but the line does not last as long. My experience has taught me that the smaller the line the shorter the lifespan.
craftsman
Keep it in a bucket with soap and water so it doesn't dry out. Pre-cut a few lengths at a time so you won't need to mess with it too often.
The return fuel line is loose or damaged. I have the same issue if you are talking the return fuel line. Here is a site I found a diagram on. http://www.ereplacementparts.com/bolens-bl100-41bd100g965-gas-string-trimmer-parts-c-27272_27749_27758.html
Weed trimmer line is made from hardened monofilament nylon of varying thicknesses. PA6/66 copolymer nylon is commonly used in weed trimmer line.