The P-P-Trap

Awesome. I just copied the idea of a P-P-trap. The idea is that you do not need to modify existing plumbing and screw this cheap device in. You can insert a filter or screen above trapped water. You can open it often to inspect without getting wet and messy.

Warning: the P-trap together with proper venting, is to avoid siphoning the water out so that sewage gas can get into the house. This device is not approved by any local codes and use it at your own risk. But I can't visualize that water in both traps are siphoned out to dry. Also, if you have your own house, the worst is that you are gased by your own sewer. Whereas in an apartment, the gas can come from everybody else.

The details: you should have a p-trap that can be unmounted, and that both parts can turn. Then this device will fit. Typically a p-trap has on one side a 1.5" union, and a 1.5" (or 1.25") slip joint on the other side. Both parts can be unscrewed and turned.

While 1.5" piping fittings are standard, slip joints are of different standards. For standard 1.5" pipes, the inside diameter is 1.5" while the outside diameter is larger. For slip joints, a 1.5" joint means that the OD of the bare pipe is 1.5", the ID of the coupling is 1.5".

The parts:
A p-trap same as what you have
A tee
A threaded male plug and female adapter
A 90 deg bend
About two 1"-2" pipe sections to joint the components

A tee is usually available in all hubs, that is, will accept standard size pipes inserted into it. You need to adapt the opening into a screwed end to accept the plug. You split your new p-trap into two at the union, and put on both ends of the tee. You only need an extra bend to join everything back together again. There are bends with one end hub and the other end bare pipe. The short pipe sections are to join the hub-to-hub. You can glue everything together in a minute or two. Positioning is easy, everything should be fair and square, no customizations needed.

When the thing is dried in 15 minutes, you can screw it into your old p-strap, split at the union. As long as the new union is the same as your old, they will fit exactly just by turning the slip joint and union.

Tips. My plug needs a little plumbing tape to make it water tight. Also my new union is different from the old union. I guest the biting angles are different. I dropped two 1.5" ID rubber seal rings and a lot of joining compound into the mismatched union to make it water proof. I suppose a seal that is a little larger than 1.5" ID and have a thick wall will do the trick without the joining compound. (The joining compound is not a glue, usually for sealing threads in place of tapes.)

For the filter trap, I rolled up a plastic mesh about 5" wide from the building department. Aluminum mesh will be perfect but they are expensive. For plastic I can throw away the filter instead of cleaning it. As the configuration in the diagram, water will push the mesh towards the plug, therefore securing it in place. Waste water will through right in the middle of the filter roll. I caught my wife pouring a little rice pudding down the drain, or is it me? No water spill out when I opened the plug, except for a few drops at the threads which is a little wider and hence lower than the pipe.

I'm sure there is water in both traps. But to be sure you can use clear PVC, and also you can see what is being trapped without opening the trap. The problem is that they are not standard, and even a piece of pipe is expensive. For example, the permaflow clear p-trap use slip joints at both ends. There are clear p-traps which is nothing more than a tee without a union. A clear tee will be good here, but it cost a lot and PVC and ABS use different cements.

I though of using clear flexible tubing. Tubing has ID 1.5" for example, which will fit 1.5" slip joints with the same OD. But if they are exactly the same you cannot insert it. Hose clamps are cheap though. The standard connection is via barbs. But the other end is usually threaded and you have to adapt it to standard slip, which the whole thing will be clumsy.

Also, to be code compliant (at least for mobile homes) you may need a check vent under the sink, between the 2 traps. It's cheap and you can screw it in instead of the plug, if it works sideways.

Applications: Currently on sale online are some traps to avoid lost of rings and ear rings. Some have a little window to look inside. This thing has a lot more screening capacity.

I see one p-trap for hair salon. This is way better and can filter more hair. You can clear it daily without dripping water.

For a proper grease trap you need a larger box. But my experience is that if you make a blind 90 deg downwards, a lot of grease will collect there. For example, if you connect a 90 deg bend to the tee instead of the plug, pointing downwards, it will collect grease. But obviously a lot more will flow away.