@davidro1, I'm not concerned with the pop-up mechanism at all. I was concerned with the pop up housing being level with the drain line. I was worried that if water stayed in the pop up housing, that the housing might be prone to leaks (at the point where the ball and rod go into the drain pipe). I was also concerned with any code issues. I remember reading somewhere that there is a maximum allowable distance the p-trap can rise from the low point to the drain line. I assumed that reversing the j-bend would result in too much of a height difference to be code compliant (I'm still assuming this, since nobody has chimed in on this issue). However, more than the legality of it all, I really just wanted to know what bad consequences might happen as a result of reversing a j-bend. @jimsonburg, Thanks for the SPAM. Not. @homebound, I was concerned about the connections. The waste arm has the flared tip, but it doesn't seem so different from the plastic washer thing that goes in the tailpiece. I've went ahead and reversed the j-trap, and everything fits fine and feels really solid. I filled up the sink, drained it all at once, and there are no leaks. I've even opened up the pop up housing (where the ball goes in) and to my surprise, there is no standing water in there (the water line sits just below that). I'll keep an eye on it to make sure nothing leaks. If it does, I'm sure we'll notice it right away, before there's any major damage. Aside from a few bottles of cleaning supplies, we don't really use the cabinet under the sink, so maybe I'll just leave an old aluminum lasagna pan down there. At least that way, it'll catch any leakage should any occur, and it will alert me to any leakage by amplifying the sound of any drips.

Maybe I have my terminology wrong. I bought a longer waste arm to extend it. Is the coupler the problem? So to make it code, I will have to find a way to access that one compression nut that held the original waste arm pipe? That means I will have to knock out some of my foundation to get to it. I can not believe it passed code the way the original plumber did it. He buried the compression nut that holds the waste arm in brick and mortar. Just a small section is exposed. I can go into the crawl space and cut the waste line where it is glued and start over. I still will have to knock out some of the foundation brick to even get the pipe and nut out but maybe not as much. Thanks for the heads up.

#1 reason for not haveing two is that there isn't enough room under most sinks. Among all the other reasons for not haveing two,the best is because one is enough.

Trap in my area is $10-20, tape $1-2, if needed flexible connections and compression fitting $20. Sometimes I think the OP does not have the skill set, materials, and tools. U tube this...if the OP is in it for the long run, subscribe to some home improvement magazines I am I in CA, Interesting in costs in other areas.