GoSwim.tv talks and demonstrates tethered swimming
Some extra ideas from Mark
We called that, "Naked paddles." Perhaps that is a bit "old school." But, it offeres some better lingo than "strapless."
I'd suggest putting the other end of the tubing much higher in the air. You need to have a good base that isn't going to get pulled into the pool, or hit others if it were to fall. And, you don't want it on the building near a window so if the belt comes off the swimmer, or the connection gets bad, or the tube should break, it won't recoil and hit a person or property -- like breaking a window. We loved hooking the end, the place that does not move, to the balcony railing. But, we also made certain that none would walk on that side of the pool. Even putting it onto the blocks is not tall enough.
A tall base helps to get over that that hip sink feeling.
Another tip / activity, put on double or triple belts. Or, just double or triple the tubing. Then it should be tight while you are at the close wall. Then the intensity is much greater. Then you can work the push-off and streamline out from the wall and underwater kick, surface and try like crazy to hit the other end. Doing that on back, side and front many times in a row is working on the jump off the walls.
Of course, the base of the tubing needs to be anchored perhaps 5 to 10 yards/meters from the near edge of the pool. Then there will be some strain just getting into the pool.
Watch out for snapping equipment! Be careful.