Two 12-foot pieces of 1-inch tubular webbing, tied in two loops (a double overhand
works well).
One 50-foot piece of 1-inch tubular webbing.
Three oval carabiners. Other carabiners also work, but the knots are easier
to get off of oval biners.
Two trees 20-30 feet apart.
Methods
First off, you'll need to know how to tie a clove hitch.
How to tie a clove hitch: (1) Make a loop. (2) Make another
loop. (3) Put the second loop behind the first loop. (4) Pull 'er tight around
that there hitchin' post (carabiner).
Now put it all together as shown in the following diagram and pictures. The tightening
mechanism (shown in the box) works off of the block-and-tackle principle. Use two carabiners
as pulleys and clip the main line through them in concentrically smaller loops.
Try to make it look nice - it works better.
The end with the tightener...
...and the other end.
To tighten, simply pull the loose end in-line with the slack line. To undo the
slack line, pull the loose end perpendicular to the slack line. It should pop free.
Results...
Here I am slacking it up at the Mayan ruins in Tikal, Guatemala.
