Designers Who Should Be Spanked: Kohler

Kohler plumbing products may look good, but, in my experience, their designs are fundamentally flawed. Consider this drain assembly that has more flaws than parts. It also happens to have more parts than it should!

Kohler Drain Design Flaws

Problem One: All Kohler drains for the 2600-series sinks have holes in the drain flange assembly to permit connection of the overflow and stopper mechanism. The 2600-series sinks don't have overflows, and stoppers are optional. Rather than selling a version of the drain flange that doesn't have those unecessary holes, Kohler includes a kit that crudely blocks those holes.

The Kohler drain assembly has holes for overflow and the stopper mechanism.

Problem Two: The Kohler kit to cover the unwanted holes uses a 2-inch length of PVC. According to my contractor, the building code in my area forbids the use of PVC in drain assemblies. Kohler provides no alternative.

Kohler provides a crude PVC sleeve the cover the holes if they aren't necessary.

Problem Three: The kit makes it very difficult to clamp the drain flange tightly to the sink basin. Getting the rubber flanges into position while maintaining proper position of the drain flange in the sink is quite the juggling act.

Tightening the assembly to the basin is difficult because of the extra gaskets and sleeve assembly.

Problem Four: The kit creates little pockets of standing water in the PVC sleeve as well as air pockets that interfere with the smooth flow of water out of the drain.

Illustration of standing water and air pockets in the PVC sleeve.

Problem Five: The drain flange and tailpiece are two distinct pieces that come preassembled. Thus they look like a single piece. The joint, which is not mentioned in the documentation, is another possible point of failure. Teflon tape should have been used in the joint to reduce the possibility of leaking.

The preassembled pieces have to be disassembled so Teflon tape can be applied.

Problem Six: The drain flange should nest inside the tailpiece, not the other way around. Water flows down, so arranging these pieces correctly would avoid leakage.

The lower pipe is nested inside the higher one, which promotes leaks.

Problem Seven: Even with two wraps of Teflon tape, the joint leaks.

Photograph and entire assembly under the sink, with water dripping from the preassembled joint.

Problem Eight: The openings in the grill over the drain are too fine, causing the water to create surface tension barriers that impede the flow of water out of the basin and the release of air trapped in the tailpiece.

Fine grill blocks the escape of the air trapped in the tailpiece.

Results: With a well-designed drain, our sinks can drain nearly as fast as the faucet can deliver the water. With the Kohler assembly, it takes 65 seconds to drain the amount of water delivered by the faucet in 10 seconds. (This is an apples-to-apples comparison with the same faucet, sink, and P-trap. The only difference is the drain flange assembly.) Furthermore, the Kohler assembly leaks through the pre-assembled threaded joint, despite two wraps of Teflon tape. (The leak occurred with two different brand-new Kohler assemblies.)

The workaround solutions are illustrated here. Install the Kohler drain after inspections so you don't get cited for using PVC in a drain assembly. Drill a tiny hole high in the PVC sleeve to allow the trapped air to escape and solve the flow problem. I used a 5/32" bit. It's important that the air release hole be high on the PVC. If it's too low, the standing water that collects in the sleeve would seep through. If the drain ever backs up, water will leak through the hole, but it's a very small hole so it'll be a small mess. Stop the leak with a more liberal application of Teflon tape.

A small hole is drilled near the top of the PVC sleeve to allow the trapped air to escape.  Teflon tape is applied liberally to block the leak.

There are several things Kohler could have done to make this a better product. First of all, they could have tested the design of the PVC kit. I can't imagine that the flow problem could have been missed even by the most casual of tests.

The flow problem could have been solved by offering a drain assembly that doesn't have the unneeded holes (they do have them for other models of lavatory basins, but not for our model). That design would then need to be tested to make sure there isn't a flow problem. Perhaps a grill with slightly larger openings would allow the air to escape straight up. Failing that, they could have provided a vent piece that fits the overflow hole rather than the PVC sleeve to cover them up. The vent would allow the air to escape. It would also be simpler to clamp the assembly to the basin without the impediment of the sleeve and extra gaskets. Either of these approaches would have resulted in fewer parts (which may translate into less manufacturing cost) and fewer potential problems (which reduces support costs) and a better experience for the installer and end-user.

Ideally, the tailpiece would not have to be a separate part from the rest of the drain assembly. Having a single piece would eliminate the possibility of leaks, but I understand the possible manufacturing advantages of having a separate tail piece. The separate piece is also easier to trim if necessary. However, any company that deals with the flow of water should understand the proper way to nest vertical pipes is to have the upper piece fit into the lower piece. Failing that, they should have provided a tighter joint by using a compression fitting. Failing that, Kohler should have sent the parts unassembled. This would increase the chance that an experienced installer would recognize the potential leak and apply Teflon tape to solve it. Failing that, the installation guide should have suggested disassembling the pieces to apply Teflon tape.

© 2002 Adrian McCarthy. All rights reserved. Aidtopia and the author(s) of these pieces don't really condone spanking designers. That phrase is meant in the figurative sense. If you really want to help, lock the aforementioned designers into a room with a copy of The Design of Everyday Things by Donald A. Norman (ISBN: 0465067107). Last updated 1-NOV-2002.