General recommendation is not to use a ski pylon for tubing. If the tube submarines at speed it will stress the pylon, possibly loosening it. At worst, pulling it out. You don't get the same stress with a skier; skier goes down and drops the tow rope. Same logic would seem to apply to a tow post.
Tow harness (bridle) that connects to the transom eyelets may be a better option. I like the kind with a pulley (Google airhead tow harness pulley).
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