Sorry for the spin! Just keep asking questions until your RPM subsides!
It is VERY important not to alienate your building dept peeps. I agree, that is a higher priority than the drain issue. After a chat with, and an "OK, go ahead" from, your PB (who (1) will have to deal with the planning dept as much or more than you and (2) might know who to talk to, or how to talk to them, based on his past permitting experiences) I would go down to the planning dept desk in person and introduce yourself. Be ultra nice and patient, and play a little dumb, non-confrontational, and have them help you with this issue. I've dealt with two different building dept staffs, and they're just people like us all that don't like being griped at and pushed around, and who appreciate someone that asks for help and treats them with respect. Then you can ask your questions and get to where you want to be.
OK next. It is my understanding that drains are used primarily for two reasons. And now-a-days really only one. Before auto-vacs and robots, people used to sweep their pools and manually vacuum them. One method was to brush from the sides down, towards the drain, and let the drain suck up debris. So yes, they can be used for cleaning, but with today's auto-cleaning systems that use is pretty much gone. The primary reason for a drain is for circulation. A properly designed pool will utilize returns and skimmers to get your water rotating in such a way that the skimmer can suck up debris, from the water as well as the surface. The "dead spots" can be down low, so the drains take up the slack. But if your returns are designed correctly, they can mix up the lower water with the upper water and improve the effectiveness of the skimmer, eliminating the need for a drain. Auto-vac systems do the rest. Proper circulation and the skimmer take care of the particulate matter throughout the pool, the vacuum takes care of the stuff on the bottom that won't "fly" into the moving water and eventually into the skimmer. Suction-side vacuum systems help additionally, as they are pulling water into the main filter from all around the bottom of the pool. Pressure-side vacs help too. That's what that tail is doing. It swishes debris off the surface into the water so circulation and the skimmer can get at it. Robots do less for circulation than the other types of vacs do, but they're still brushing and agitating down low, to help the skimming. And all vacs are collecting debris, big and small, all along the bottom. So between a well-designed set of returns, and a vacuum, needing a drain for circulation is not necessary.
The exception to all this is big, commercial pools, where drains are more commonly required (and codes mandate them). The pool is too big and wide, with too much bather load, to get away with no drains. The drains create the circulation necessary out away from the skimmers where there are way more dead spots than in a smaller residential pool. Which is very unfortunate, because a lot of the drain accidents happen in commercial pools.
Draining a pool using the drain and your pool pump is not usually done. And there is no need to do it that way. (Why the heck to they call them drains, then!?!) If you have to remove the water, you throw in a small portable pump with a big hose and drain through that. It's way more efficient, and solves the very real problem of what happens at the end. When it finishes at 4 am and you're sound asleep, those portable pumps have sensors that shut themselves off. Your main pump? Not so much. It'll run dry and could overheat. Some have safeguards for that, but you gamble on that with a $50 portable, not a $1000 VS pump!
So drains are for circulation, and IMHO the danger they introduce into your pool is not worth having them, not when you can add a few returns down low and get rid of them all together. That, I believe, is why the trend now is to build pools without them.
But here's the biggie (now that we've conquered the building dept), your PB needs to be on board with this plan, and more importantly, know how to design a drain-less circulation system. That's critical, and part of your discussion with him before you go down to the planning dept.
With me so far?
If MinerJason is right, and you don't need drains (and don't want drains) then all your questions about "2 outlets and separation and vertical planes" are moot. Forget all that.
If you do decide to eliminate drains, you have one more consideration in terms of safety. The vacuum port. If it were my pool, I would plumb in a vacuum port. As another wrote, even with his robot, he uses that port for spot vacuuming. So with that port, you'll have all your options. It can be used for spot vacuuming. It can be used for suction-side vacuuming. It can be replumbed at the pad to accommodate pressure-side systems, and it can be left unused at all if you go with a robot. You can buy a $500 vac now, and use the port. Then you can switch to a robot when you're ready and ignore the port. Or you can use it to manually vacuum the pool until you decide what auto system you want to splurge on.
That said, as I pointed out before, a vacuum port can be just as dangerous as a drain, even more so, because it is closer to the surface and its very concentrated suction as compared to a drain cover. They have been known to eviscerate a person. Yep, sorry to have to paint that picture. I describe in a previous post how to get around most of that danger, but if you want the safest possible pool, you leave that out. Or install it just to have it, but you take off its outer fitting and screw in a plug that would render it suck-proof (unless your kids swim around with a crescent wrench!).
If I've completely misunderstood your post, and you decide (or have already decided) you do want a drain after all, then we can revisit all your questions about drain configurations...
Edit:
I just reread this and I was a bit misleading. Circulation
is cleaning, so to the extent drains help circulation, yes, they are still used for cleaning. What I meant by "they are no longer used for cleaning" was the "old style" cleaning, where crud was pushed into them with a brush.
