IKEA Left Out This Key Detail You Should Know When Installing Their Sinks
When are verbal instructions actually worse than IKEA's wordless assembly guidance? If that sounds like the setup for a joke, unfortunately it's not. When it comes to plumbing a bathroom sink drain, it might actually be less useful to have written instructions. There are many ways to go wrong when buying a new sink. This particular problem starts about where your sink drainpipe enters the wall and an adapter might be required in order to make 1 ½-inch pipes fit 1 ½-inch pipes. IKEA offers essentially no guidance on this in its assembly instructions for bathroom sinks, which homeowners understandably find frustrating.
The problem is that the pipes immediately connected to your sink drain — the p trap and its neighbors, usually made of thin polypropylene, chrome, or chromed polypropylene — aren't sized the same way as in-wall metal and PVC drainpipes. A 1 ½-inch polypro pipe is described by its outer diameter, while a 1 ½-inch schedule 40 PVC pipe has a nominal size that doesn't match its inner or outer diameter. To make matters worse, not all sink-side pipes are 1 ½ inches, and there's no commonly accepted name for them. Many refer to their joints as "slip" connectors, but that term is also used for threadless PVC pipes. Oatey calls them "tubular," Ace Hardware calls them "D slip," True Value sensibly affixes "OD" to the size, and many sellers don't bother differentiating them at all.
Even the solution goes by two names. It's as if the universe is determined to keep you from hooking up your new sink. The good news is that all you need is something called a trap adapter, occasionally referred to as a Marvel adapter.
Which trap adapter do you need?
After wading through the needless complexity of sink drains, it's understandable if you feel a mild panic when you hear that there are multiple trap adapters you'll have to choose from. But don't worry: In most cases, it's a fairly simple thing to sort out for both installing kitchen sink drains and installing or replacing a bathroom sink drain.
Trap adapters are designed to fit polypropylene tubes on the sink side and PVC (and occasionally metal) slip joints or pipe threads on the other. All you have to do is figure out which you have. The polypropylene side is simple, because the outer diameter of those pipes match the name you'll find on hardware store shelves. That is, a 1 ½-inch diameter pipe is called a "1 ½-inch pipe." Imagine that. The sink side of the trap adapter is most often 1 ¼ inches, but IKEA sinks are all 1 ½ inches. Meanwhile, the PVC side is often marked on the pipe (it's usually 1 ½ inches), but you can measure it carefully and determine which adapter you need.
There is one case in which a trap adapter won't be necessary, and that's when you connect your polypropylene drain tubes to existing polypropylene drain tubes. If these don't instantly fit together, take a single photo of the two parts you're trying to join and take it to your hardware seller of choice and they'll give you what you need. The easiest way to deal with these couplings is often to buy one of the newer (and pricier) push-to-connect fittings like Keeney's Insta-Plumb 1 ½-inch and 1 ¼-inch trap adapters.