Thanks, here is a picture of the concrete with the measurement from old to new. It would be closer to 18" to the actual intake drain. The tub is Woodbridge Venezia 31.5-in W x 71-in L Acrylic Oval Center Drain Freestanding Whirlpool and Air Bath Combination Tub. It has an integrated overflow.

Item #3837858Model #LB180

You bought the wrong tub type for the application. Return it and buy a tub that fits the unalterable specs of the actual space that you have.

Thanks Verbo, I realize the challenges after my purchase. Was hoping that is not my only alternative.

You can't run it 18" at the proper slope in that 4.25" space? You need 1.5 (ft) x 0.25" per foot = or 3/8" of drain slope. Or does the existing drain end up outside the footprint of the new tub?

Thanks palimpsest, for your input. I think you are saying what I hope will work. What I proposed to my plumber's assistant was that if the pipe length is 18" from the existing hole in the concrete to the new tub drain, the fall is less than an inch. If the diameter of the drain pipe is 1 1/2", shouldn't I be able to do that inside the 4 1/2" space that is under the new tub's skirting? And to answer your question, the footprint is all under the new tub.

We are looking to do the same, did this work adding an extension? if do, what did they use?

Hi Kim, I feel your pain! I was not able to find a plumber who could or would do what I had planned. The fitting that is found in google searches is not legal per our plumbing code. I redesigned my space to accommodate my restrictions and have a different tub. Others in our building put in a platform to raise the tub. Hope that helps.