I think any tub should be filled with water to a certain level, usually, you fill water to about 2 to 3" inches above the top of the jets and each manufacturer tells you "Do not fill the tub above a certain level". because when you crank the jets and a person gets in the tub the water will naturally rise. That said the tub in question the so-called "vent pipe" should be and it looks like it is above the overflow drain so I don't see how that tub can be filled above overflow drain to cause the vent pipe to overflow.

Greg, thanks for the perspective. If I may ask a clarifying question, please. I agree that under most circumstances the tub will be filled to or below the overflow drain. However, assume that the tub is unoccupied and the water fills to the overflow - now someone gets in and the water rises above the overflow. If it rises above the deck, then obviously it will spill over the side and onto the floor, but if it rises to a level just below the deck the tub, it will appear from the outside that nothing is spilling, yet below the deck water will be flowing out of the vent pipe. I acknowledge that under normal operation the water doesn't rise above the overflow - but hopefully you can agree that sometimes it may rise above, and when it does - this tub will leak underneath, in the sealed-off and invisible space. Is that considered an acceptable risk? Or is the sealed off space below the tub supposed to stay dry?

That's why they say that assumption is the mother of all the screw-ups... If you fill the regular bathtub the water will go over the edge also, and so is a cup of tea if you fill to the rim and drop a lemon it will go over the edge.

This way you cannot fill it over the overflow that is the purpose of it.

That being said, I have never seen a vent pipe like this, and I installed lots of jacuzzies and never had an issue of overflow or have vent pipes under the tub.

Thanks. I am thinking I need to find a different tub, one does doesn't have open pipes that can leak underneath. Is there a similar looking jet tub that you could recommend, please?

There are many similar tubs by Kohler, Jacuzzi, etc in many price ranges, I'm sure there are plenty of similar tubs out there.

Good luck

So, why don't you take some pipe and fittings and extend those two vertical standpipes horizontally and then upward into the adjacent wall cavity, terminating them 6" above the deck of the tub. Then, when you over fill the tub, the standpipes won't leak and you will get the water on the floor where you want it.

What is the length of your tub? You may want to take a look at Bain Ultra. They are the leader in the industry when it comes to air tubs