I am looking for a hitch to tie in webbing.
Perhaps, but really you're looking for relief from a current
system you find challenging with regard to untying --and
maybe a different structure is a better solution than some hitch!

Such a cool application of the versatackle, especially when it locks itself off.
Realize that the locking-off aspect comes at a price
--friction, that greatly diminishes mechanical advantage.
But, it it's adequate for your application, great.
Let me suggest a change to the overall slackline structure
that will eliminate not only your added carabiner but will
rearrange the others:
A) Attach one end of the line directly to the tree, using at
least one full wrap --maybe two is better-- and then maybe
clipping a 'biner (tied to tail) around this line (else, lose the
'biner and finish like a
timber hitch dogging the tail under
some wraps after turning it around the 2-B-tensioned line.
B) With the slackline tied to a 'biner in its other end
(and your suggestion of trying a
pile hitch I think is good),
anchor this end to the tree by running the sling bight
through the 'biner, and then conjoining ends of this
sling with the
versatackle tensioning structure. Thus, you have
some pseudo-2:1 hauling advantage (less, via friction) added
to that of the
versatackle's --and you can work that with
cord, and tie off the cord easily, in various places.
Now, your slacklne as sketched above --i.e., that piece of tape
(or rope) on which you're walking-- has 'biners in both *ends*,
one of which will need to be adjustably placed (unless you work
the same two trees always); the one that could be replaced
with a
timber hitch will be the one with much less load on it.
One last thing, we use a water knot to make a ring of webbing
that wraps around the tree/post/pole (red in the diagram) and would like a
knot that doesn't jam for that too, if anyone has any ideas.
Here, again, one might back up a little and consider the entire
system and how it's used, to seek a solution. Let me suggest
that you tie off with the
offset fig.8 bend --what might be warned
against (as an abseil-ropes joint) as the "EDK-8"-- such that
you carefully place this knot as the bight-tip of a
pile hitchto one 'biner (of my above system). And *slip* the knot, for
both some aid in untying, and in giving extra bulk for the
stopper. So, you'd join your sling-tape tails with this knot
and position it at just the right point of a
pile hitch to a 'biner,
with the 2nd 'biner (for you tensioning
versatackle, as described
above) simply clipped into the sling.
(But, in the usual case --as your first URLink shows--, one could
still tie off the tails in this way, to the LONE 'biner, and then
just clip in the opposite end of the sling atop this.)
((So, this way of closing the sling entails a 'biner, either way,
and isn't a general solution.))
QED,
--dl*
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