I need to replace a tub, and of course the replacement has slightly different rough-in dimensions than the old tub. The location of the current trap won't work with the new tub, but there is room to place it downstream (within 2-feet of the tub drain horizontally, and one foot vertically). This would put the trap about one foot down stream of the vent (this is the only fixture on this drain/vent line). I've looked in the plumbing codes but haven't found if this is allowable.

First, install tub, trap and drain. Connect with existing with San-T. THEN, worry about vent: extend vent from top of new San T towards old vent. Reconnect.

I don't understand how is it that new and old tub won't line up. They usually do - as long as you are not installing large whirlpool tub in place or regular tub or vice-versa. Basic drain and overflow dimensions remain same for over 125 years since John Michael Kohler began manufacturing his trade mark - Cast Iron tubs, as we know it today - that set industry standards.

the replacement has slightly different rough-in dimensions than the old tub Most tubs rough in at 60 inches. What makes yours different? Let me know. Tom

Sorry guys. Once again, you didn't receive all the info. Here is a picture of what was there once the old tub was removed. The trap was attached directly to the tub drain, and there was no overflow. There is about 8.5" between the 90° ell and the tee. I have not set the new tub in yet to see how all of this jives, but based on dimensions, the existing drain needs to be below the floor decking, and the overflow will be right against the floor joist in the picture. Base assumption is the trap should be downstream of the overflow, which will also put it downstream of the existing vent. Hence the original question...

It appears to me that the old tub was not a regular tub. The way it is set up - it still could have overflow installed. It got removed with the tub.

Now, what EXACTLY do you want to install there now... Please, be generous with words.

No, the overflow was not taken out with the old tub. There was no overflow. Regardless of that or getting caught up in what I want to install, I would just like the answer to the question... Can the fixture trap be downstream of the fixture vent and meet code?