Early adopters are the guinea pigs, fruit flies, lab rats. Plumbers are always willing to look at new things. Plumbers are reluctant to adopt new things, because a lot of study has already gone into the products and rules that we now have. Many new products cause other problems. When a product is marketed to the general public and not to plumbers alone, it is a clue that there may be a reason why plumbers have not accepted this innovation. P traps already have the self-scouring ability described in the video now on permaflow-drain.com page 1. ("creates turbulence"). This is described in plumbing codes also, because there is a size limit to prevent anyone from oversizing the P trap or pipe. (Pipe too large = ensures stuff gets deposited and not carried downstream. (which is the opposite of our intentions).). The paddle in the permaflow might be a great advantage. Or, it might cause other problems which we will know as common knowledge in 20 years from now. The Permaflow being transparent is a nice feature, which other P traps could also have. Maybe there are transparent regular P traps already. I've not gone looking. P traps are already made with holes underneath that you can open to clean them out from. (It's a threaded hole with a bolt to seal it. You leave it closed for years at a time). To see an image of one, search for "P-Trap with Cleanout". It has a huge advantage over the permaflow: you remove gravel sand dust and gunk that might have been dropped down the drain during construction or during the course of normal living. Why do people not install them more often? I don't know. What I do know is that it is far far better to remove things that collect in the P trap than to send them a few feet downstream. The permaflow merely gives you a paddle that sends blockages downstream a few feet. It does not guarantee that objects will be carried out of your house's DWV drain line and into the public sewer or into your septic tank. Another concern I see right now is that the paddle has a handle outside the drain, on an axis which pierces the drain --- so this is where a drip can occur. My initial conclusion is that I would like to have a clear plastic P trap. If it had a cleanout that I open up entirely, I would have the option to remove stuff too. On the other hand, maybe clear plastic is not yet good enough to be truly useful as P trap material: maybe it cracks or cannot be glued well to the other materials, or... well, I'll find out within the next 20 years. Stay tuned. hth

Your current configuration has a number of code violations. You have a regular Tee connecting the two drains but code requires a baffled tee: Ref IRC-2707.1 & UPC-405.4: Directional fittings are required for continuous wastes from a disposal or Dishwasher (I.E. Wyes, ComboÂs or TeeÂs with baffles). Your Tee is connected by means of slip joints: Ref. IRC-3201.1 & UPC-1002.3: Maximum of one (1) slip joint on the outlet side of a P-trap NOTE: slip joint type P-traps and waste fittings are made to Tube Standard and the single slip joint permitted on the discharge side of the P-trap is the "Trap Adapter" that transitions the slip joint tubing to the Pipe size to match the drain piping in the wall. You can rule out looking for a higher P-trap because P-traps are made to ASTM specification and they are all the same. Increasing the height of the P-trap would increase the water level in the trap above the code maximum of 4". THE POSILBE SOLUTIONS: 1. Install the exact same make and model of disposal and waste kit as was originally installed. 2. Remove the factory supplied ¼ bend on the disposal output and use a Disposal Type" end waste kit. (An ordinary end waste kit has a molded ¼ bend on the cross tube that is intended to be connected to a sink drain tailpiece. A "Disposal Type" end waste kit has a straight cross tube with a flange connection on the input end. The factory supplied ¼ bend in the disposal kit is discarded and the cross tube is connected directly to the disposal port. This keeps the cross tube about 3" to 4" higher. The disposal type end waste kit comes with the code required baffled Tee.) 3. Open the wall and lower the elevation of the waste arm. 4. If you are under the IRC and if the waste arm is a 2" pipe you could cut the trap adapter off the waste arm then install a Wye with a trap adapter on the end and the side port, then install separate traps from each sink. (Note: It must be a 2" waste arm because if you install separate traps the load must be computed as separate sinks with a 3DFU value for each trap. Under the IRC the maximum permissible load on an 1-1/2" line is 3DFU however if it is a 2" line the maximum load is 6DFU and separate traps would be permitted. (Note-The UPC prohibits connecting two traps to a common waste arm)

The guy at Home Depot just proved to you why he is stocking shelves instead of working in the plumbing trade. Using an 1-1/2" trap as suggest by the Home Depot clerk would be two code violations. 1. A shower is required to have a 2" trap and a 2" drain line & 2. The drain basket in the base of the shower already has a 2" discharge and code strictly prohibits reducing the size of a drain line in the direction of flow. You may need to consult a framer about sistering that joist so you can notch it. The plumbing code prohibits any notches on the top of a floor joist in the center 1/3 of the overall span. On the outer 1/3 of the joist you may notch to a depth not to exceed 1/6 the height of the joist. (a 2x10 could be notched a maximum of 1-1/2").

@Richard Thomas... That's so wrong on so many different levels... if the sewer backs up from a non siphon type of back up then it will flow up and into the drain line. Second, you don't install the air gap behind the p trap. You install it BEFORE the P trap. On the down tube of the sink. But 99% of ppl with an air gap use garbage disposals so that's mostly irrelevant. Also yes I know this thread is old but this info is RELEVANT and can save many others from headaches. Yes a kink or clog will cause water to spew out of the air gap cap but with this older design most of the "trickle leaks" that seem to come from nowhere or underneath actually come from the second set of inner threads that the cap screws down onto. NOT the outer threads that bolt to the sink. Anyways, THE OPs DESIGN OF AIR GAP HAS A DESIGN FLAW. THE THREADS INSIDE WHERE THE INNER CAP TWISTS DOWN GET STRIPPED OVER THE YEARS AND IT STARTS LEAKING FROM THE INSIDE DOWN. It has nothing to do with anything else. Get the other ONE PIECE BODY design. Also for others saying just ditch the air gap. NOT EVERYONE WANTS TO JUST DITCH THE AIR GAP NOR CAN THEY BECAUSE IT'S AGAINST CODE IN MANY STATES.